[ Upstream commit 15f389da11257b806da75a070cfa41ca0cc15aae ]
Samsung DSIM used in older Exynos SoCs (like Exynos 4210, 4x12, 3250)
doesn't report empty level of packer header FIFO. In case of those SoCs,
use the old way of waiting for empty command tranfsfer FIFO, removed
recently by commit 14806c6415 ("drm: bridge: samsung-dsim: Drain command transfer FIFO before transfer").
Fixes: 14806c6415 ("drm: bridge: samsung-dsim: Drain command transfer FIFO before transfer")
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Marek Vasut <marex@denx.de>
Signed-off-by: Robert Foss <rfoss@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230809145641.3213210-1-m.szyprowski@samsung.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
when using __drm_kunit_helper_alloc_drm_device() the driver may be
dereferenced by device-managed resources up until the device is
freed, which is typically later than the kunit-managed resource code
frees it. Fix this by simply make the driver device-managed as well.
In short, the sequence leading to the UAF is as follows:
INIT:
Code allocates a struct device as a kunit-managed resource.
Code allocates a drm driver as a kunit-managed resource.
Code allocates a drm device as a device-managed resource.
EXIT:
Kunit resource cleanup frees the drm driver
Kunit resource cleanup puts the struct device, which starts a
device-managed resource cleanup
device-managed cleanup calls drm_dev_put()
drm_dev_put() dereferences the (now freed) drm driver -> Boom.
Related KASAN message:
[55272.551542] ==================================================================
[55272.551551] BUG: KASAN: slab-use-after-free in drm_dev_put.part.0+0xd4/0xe0 [drm]
[55272.551603] Read of size 8 at addr ffff888127502828 by task kunit_try_catch/10353
[55272.551612] CPU: 4 PID: 10353 Comm: kunit_try_catch Tainted: G U N 6.5.0-rc7+ #155
[55272.551620] Hardware name: ASUS System Product Name/PRIME B560M-A AC, BIOS 0403 01/26/2021
[55272.551626] Call Trace:
[55272.551629] <TASK>
[55272.551633] dump_stack_lvl+0x57/0x90
[55272.551639] print_report+0xcf/0x630
[55272.551645] ? _raw_spin_lock_irqsave+0x5f/0x70
[55272.551652] ? drm_dev_put.part.0+0xd4/0xe0 [drm]
[55272.551694] kasan_report+0xd7/0x110
[55272.551699] ? drm_dev_put.part.0+0xd4/0xe0 [drm]
[55272.551742] drm_dev_put.part.0+0xd4/0xe0 [drm]
[55272.551783] devres_release_all+0x15d/0x1f0
[55272.551790] ? __pfx_devres_release_all+0x10/0x10
[55272.551797] device_unbind_cleanup+0x16/0x1a0
[55272.551802] device_release_driver_internal+0x3e5/0x540
[55272.551808] ? kobject_put+0x5d/0x4b0
[55272.551814] bus_remove_device+0x1f1/0x3f0
[55272.551819] device_del+0x342/0x910
[55272.551826] ? __pfx_device_del+0x10/0x10
[55272.551830] ? lock_release+0x339/0x5e0
[55272.551836] ? kunit_remove_resource+0x128/0x290 [kunit]
[55272.551845] ? __pfx_lock_release+0x10/0x10
[55272.551851] platform_device_del.part.0+0x1f/0x1e0
[55272.551856] ? _raw_spin_unlock_irqrestore+0x30/0x60
[55272.551863] kunit_remove_resource+0x195/0x290 [kunit]
[55272.551871] ? _raw_spin_unlock_irqrestore+0x30/0x60
[55272.551877] kunit_cleanup+0x78/0x120 [kunit]
[55272.551885] ? __kthread_parkme+0xc1/0x1f0
[55272.551891] ? __pfx_kunit_try_run_case_cleanup+0x10/0x10 [kunit]
[55272.551900] ? __pfx_kunit_generic_run_threadfn_adapter+0x10/0x10 [kunit]
[55272.551909] kunit_generic_run_threadfn_adapter+0x4a/0x90 [kunit]
[55272.551919] kthread+0x2e7/0x3c0
[55272.551924] ? __pfx_kthread+0x10/0x10
[55272.551929] ret_from_fork+0x2d/0x70
[55272.551935] ? __pfx_kthread+0x10/0x10
[55272.551940] ret_from_fork_asm+0x1b/0x30
[55272.551948] </TASK>
[55272.551953] Allocated by task 10351:
[55272.551956] kasan_save_stack+0x1c/0x40
[55272.551962] kasan_set_track+0x21/0x30
[55272.551966] __kasan_kmalloc+0x8b/0x90
[55272.551970] __kmalloc+0x5e/0x160
[55272.551976] kunit_kmalloc_array+0x1c/0x50 [kunit]
[55272.551984] drm_exec_test_init+0xfa/0x2c0 [drm_exec_test]
[55272.551991] kunit_try_run_case+0xdd/0x250 [kunit]
[55272.551999] kunit_generic_run_threadfn_adapter+0x4a/0x90 [kunit]
[55272.552008] kthread+0x2e7/0x3c0
[55272.552012] ret_from_fork+0x2d/0x70
[55272.552017] ret_from_fork_asm+0x1b/0x30
[55272.552024] Freed by task 10353:
[55272.552027] kasan_save_stack+0x1c/0x40
[55272.552032] kasan_set_track+0x21/0x30
[55272.552036] kasan_save_free_info+0x27/0x40
[55272.552041] __kasan_slab_free+0x106/0x180
[55272.552046] slab_free_freelist_hook+0xb3/0x160
[55272.552051] __kmem_cache_free+0xb2/0x290
[55272.552056] kunit_remove_resource+0x195/0x290 [kunit]
[55272.552064] kunit_cleanup+0x78/0x120 [kunit]
[55272.552072] kunit_generic_run_threadfn_adapter+0x4a/0x90 [kunit]
[55272.552080] kthread+0x2e7/0x3c0
[55272.552085] ret_from_fork+0x2d/0x70
[55272.552089] ret_from_fork_asm+0x1b/0x30
[55272.552096] The buggy address belongs to the object at ffff888127502800
which belongs to the cache kmalloc-512 of size 512
[55272.552105] The buggy address is located 40 bytes inside of
freed 512-byte region [ffff888127502800, ffff888127502a00)
[55272.552115] The buggy address belongs to the physical page:
[55272.552119] page:00000000af6c70ff refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x127500
[55272.552127] head:00000000af6c70ff order:3 entire_mapcount:0 nr_pages_mapped:0 pincount:0
[55272.552133] anon flags: 0x17ffffc0010200(slab|head|node=0|zone=2|lastcpupid=0x1fffff)
[55272.552141] page_type: 0xffffffff()
[55272.552145] raw: 0017ffffc0010200 ffff888100042c80 0000000000000000 dead000000000001
[55272.552152] raw: 0000000000000000 0000000080200020 00000001ffffffff 0000000000000000
[55272.552157] page dumped because: kasan: bad access detected
[55272.552163] Memory state around the buggy address:
[55272.552167] ffff888127502700: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[55272.552173] ffff888127502780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[55272.552178] >ffff888127502800: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[55272.552184] ^
[55272.552187] ffff888127502880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[55272.552193] ffff888127502900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[55272.552198] ==================================================================
[55272.552203] Disabling lock debugging due to kernel taint
v2:
- Update commit message, add Fixes: tag and Cc stable.
v3:
- Further commit message updates (Maxime Ripard).
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: David Airlie <airlied@gmail.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: dri-devel@lists.freedesktop.org
Cc: stable@vger.kernel.org # v6.3+
Fixes: d987803107 ("drm/tests: helpers: Allow to pass a custom drm_driver")
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Francois Dugast <francois.dugast@intel.com>
Acked-by: Maxime Ripard <mripard@kernel.org>
Link: https://lore.kernel.org/r/20230907135339.7971-2-thomas.hellstrom@linux.intel.com
Signed-off-by: Maxime Ripard <mripard@kernel.org>
If *any* object of a certain WW mutex class is locked, lockdep will
consider *all* mutexes of that class as locked. Also the lock allocation
tracking code will apparently register only the address of the first
mutex of a given class locked in a sequence.
This has the odd consequence that if that first mutex is unlocked while
other mutexes of the same class remain locked and then its memory then
freed, the lock alloc tracking code will incorrectly assume that memory
is freed with a held lock in there.
For now, work around that for drm_exec by releasing the first grabbed
object lock last.
v2:
- Fix a typo (Danilo Krummrich)
- Reword the commit message a bit.
- Add a Fixes: tag
Related lock alloc tracking warning:
[ 322.660067] =========================
[ 322.660070] WARNING: held lock freed!
[ 322.660074] 6.5.0-rc7+ #155 Tainted: G U N
[ 322.660078] -------------------------
[ 322.660081] kunit_try_catch/4981 is freeing memory ffff888112adc000-ffff888112adc3ff, with a lock still held there!
[ 322.660089] ffff888112adc1a0 (reservation_ww_class_mutex){+.+.}-{3:3}, at: drm_exec_lock_obj+0x11a/0x600 [drm_exec]
[ 322.660104] 2 locks held by kunit_try_catch/4981:
[ 322.660108] #0: ffffc9000343fe18 (reservation_ww_class_acquire){+.+.}-{0:0}, at: test_early_put+0x22f/0x490 [drm_exec_test]
[ 322.660123] #1: ffff888112adc1a0 (reservation_ww_class_mutex){+.+.}-{3:3}, at: drm_exec_lock_obj+0x11a/0x600 [drm_exec]
[ 322.660135]
stack backtrace:
[ 322.660139] CPU: 7 PID: 4981 Comm: kunit_try_catch Tainted: G U N 6.5.0-rc7+ #155
[ 322.660146] Hardware name: ASUS System Product Name/PRIME B560M-A AC, BIOS 0403 01/26/2021
[ 322.660152] Call Trace:
[ 322.660155] <TASK>
[ 322.660158] dump_stack_lvl+0x57/0x90
[ 322.660164] debug_check_no_locks_freed+0x20b/0x2b0
[ 322.660172] slab_free_freelist_hook+0xa1/0x160
[ 322.660179] ? drm_exec_unlock_all+0x168/0x2a0 [drm_exec]
[ 322.660186] __kmem_cache_free+0xb2/0x290
[ 322.660192] drm_exec_unlock_all+0x168/0x2a0 [drm_exec]
[ 322.660200] drm_exec_fini+0xf/0x1c0 [drm_exec]
[ 322.660206] test_early_put+0x289/0x490 [drm_exec_test]
[ 322.660215] ? __pfx_test_early_put+0x10/0x10 [drm_exec_test]
[ 322.660222] ? __kasan_check_byte+0xf/0x40
[ 322.660227] ? __ksize+0x63/0x140
[ 322.660233] ? drmm_add_final_kfree+0x3e/0xa0 [drm]
[ 322.660289] ? _raw_spin_unlock_irqrestore+0x30/0x60
[ 322.660294] ? lockdep_hardirqs_on+0x7d/0x100
[ 322.660301] ? __pfx_kunit_try_run_case+0x10/0x10 [kunit]
[ 322.660310] ? __pfx_kunit_generic_run_threadfn_adapter+0x10/0x10 [kunit]
[ 322.660319] kunit_generic_run_threadfn_adapter+0x4a/0x90 [kunit]
[ 322.660328] kthread+0x2e7/0x3c0
[ 322.660334] ? __pfx_kthread+0x10/0x10
[ 322.660339] ret_from_fork+0x2d/0x70
[ 322.660345] ? __pfx_kthread+0x10/0x10
[ 322.660349] ret_from_fork_asm+0x1b/0x30
[ 322.660358] </TASK>
[ 322.660818] ok 8 test_early_put
Cc: Christian König <christian.koenig@amd.com>
Cc: Boris Brezillon <boris.brezillon@collabora.com>
Cc: Danilo Krummrich <dakr@redhat.com>
Cc: dri-devel@lists.freedesktop.org
Fixes: 09593216bf ("drm: execution context for GEM buffers v7")
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Danilo Krummrich <dakr@redhat.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230906095039.3320-4-thomas.hellstrom@linux.intel.com
Pull drm updates from Dave Airlie:
"The drm core grew a new generic gpu virtual address manager, and new
execution locking helpers. These are used by nouveau now to provide
uAPI support for the userspace Vulkan driver. AMD had a bunch of new
IP core support, loads of refactoring around fbdev, but mostly just
the usual amount of stuff across the board.
core:
- fix gfp flags in drmm_kmalloc
gpuva:
- add new generic GPU VA manager (for nouveau initially)
syncobj:
- add new DRM_IOCTL_SYNCOBJ_EVENTFD ioctl
dma-buf:
- acquire resv lock for mmap() in exporters
- support dma-buf self import automatically
- docs fixes
backlight:
- fix fbdev interactions
atomic:
- improve logging
prime:
- remove struct gem_prim_mmap plus driver updates
gem:
- drm_exec: add locking over multiple GEM objects
- fix lockdep checking
fbdev:
- make fbdev userspace interfaces optional
- use linux device instead of fbdev device
- use deferred i/o helper macros in various drivers
- Make FB core selectable without drivers
- Remove obsolete flags FBINFO_DEFAULT and FBINFO_FLAG_DEFAULT
- Add helper macros and Kconfig tokens for DMA-allocated framebuffer
ttm:
- support init_on_free
- swapout fixes
panel:
- panel-edp: Support AUO B116XAB01.4
- Support Visionox R66451 plus DT bindings
- ld9040:
- Backlight support
- magic improved
- Kconfig fix
- Convert to of_device_get_match_data()
- Fix Kconfig dependencies
- simple:
- Set bpc value to fix warning
- Set connector type for AUO T215HVN01
- Support Innolux G156HCE-L01 plus DT bindings
- ili9881: Support TDO TL050HDV35 LCD panel plus DT bindings
- startek: Support KD070FHFID015 MIPI-DSI panel plus DT bindings
- sitronix-st7789v:
- Support Inanbo T28CP45TN89 plus DT bindings
- Support EDT ET028013DMA plus DT bindings
- Various cleanups
- edp: Add timings for N140HCA-EAC
- Allow panels and touchscreens to power sequence together
- Fix Innolux G156HCE-L01 LVDS clock
bridge:
- debugfs for chains support
- dw-hdmi:
- Improve support for YUV420 bus format
- CEC suspend/resume
- update EDID on HDMI detect
- dw-mipi-dsi: Fix enable/disable of DSI controller
- lt9611uxc: Use MODULE_FIRMWARE()
- ps8640: Remove broken EDID code
- samsung-dsim: Fix command transfer
- tc358764:
- Handle HS/VS polarity
- Use BIT() macro
- Various cleanups
- adv7511: Fix low refresh rate
- anx7625:
- Switch to macros instead of hardcoded values
- locking fixes
- tc358767: fix hardware delays
- sitronix-st7789v:
- Support panel orientation
- Support rotation property
- Add support for Jasonic JT240MHQS-HWT-EK-E3 plus DT bindings
amdgpu:
- SDMA 6.1.0 support
- HDP 6.1 support
- SMUIO 14.0 support
- PSP 14.0 support
- IH 6.1 support
- Lots of checkpatch cleanups
- GFX 9.4.3 updates
- Add USB PD and IFWI flashing documentation
- GPUVM updates
- RAS fixes
- DRR fixes
- FAMS fixes
- Virtual display fixes
- Soft IH fixes
- SMU13 fixes
- Rework PSP firmware loading for other IPs
- Kernel doc fixes
- DCN 3.0.1 fixes
- LTTPR fixes
- DP MST fixes
- DCN 3.1.6 fixes
- SMU 13.x fixes
- PSP 13.x fixes
- SubVP fixes
- GC 9.4.3 fixes
- Display bandwidth calculation fixes
- VCN4 secure submission fixes
- Allow building DC on RISC-V
- Add visible FB info to bo_print_info
- HBR3 fixes
- GFX9 MCBP fix
- GMC10 vmhub index fix
- GMC11 vmhub index fix
- Create a new doorbell manager
- SR-IOV fixes
- initial freesync panel replay support
- revert zpos properly until igt regression is fixeed
- use TTM to manage doorbell BAR
- Expose both current and average power via hwmon if supported
amdkfd:
- Cleanup CRIU dma-buf handling
- Use KIQ to unmap HIQ
- GFX 9.4.3 debugger updates
- GFX 9.4.2 debugger fixes
- Enable cooperative groups fof gfx11
- SVM fixes
- Convert older APUs to use dGPU path like newer APUs
- Drop IOMMUv2 path as it is no longer used
- TBA fix for aldebaran
i915:
- ICL+ DSI modeset sequence
- HDCP improvements
- MTL display fixes and cleanups
- HSW/BDW PSR1 restored
- Init DDI ports in VBT order
- General display refactors
- Start using plane scale factor for relative data rate
- Use shmem for dpt objects
- Expose RPS thresholds in sysfs
- Apply GuC SLPC min frequency softlimit correctly
- Extend Wa_14015795083 to TGL, RKL, DG1 and ADL
- Fix a VMA UAF for multi-gt platform
- Do not use stolen on MTL due to HW bug
- Check HuC and GuC version compatibility on MTL
- avoid infinite GPU waits due to premature release of request memory
- Fixes and updates for GSC memory allocation
- Display SDVO fixes
- Take stolen handling out of FBC code
- Make i915_coherent_map_type GT-centric
- Simplify shmem_create_from_object map_type
msm:
- SM6125 MDSS support
- DPU: SM6125 DPU support
- DSI: runtime PM support, burst mode support
- DSI PHY: SM6125 support in 14nm DSI PHY driver
- GPU: prepare for a7xx
- fix a690 firmware
- disable relocs on a6xx and newer
radeon:
- Lots of checkpatch cleanups
ast:
- improve device-model detection
- Represent BMV as virtual connector
- Report DP connection status
nouveau:
- add new exec/bind interface to support Vulkan
- document some getparam ioctls
- improve VRAM detection
- various fixes/cleanups
- workraound DPCD issues
ivpu:
- MMU updates
- debugfs support
- Support vpu4
virtio:
- add sync object support
atmel-hlcdc:
- Support inverted pixclock polarity
etnaviv:
- runtime PM cleanups
- hang handling fixes
exynos:
- use fbdev DMA helpers
- fix possible NULL ptr dereference
komeda:
- always attach encoder
omapdrm:
- use fbdev DMA helpers
ingenic:
- kconfig regmap fixes
loongson:
- support display controller
mediatek:
- Small mtk-dpi cleanups
- DisplayPort: support eDP and aux-bus
- Fix coverity issues
- Fix potential memory leak if vmap() fail
mgag200:
- minor fixes
mxsfb:
- support disabling overlay planes
panfrost:
- fix sync in IRQ handling
ssd130x:
- Support per-controller default resolution plus DT bindings
- Reduce memory-allocation overhead
- Improve intermediate buffer size computation
- Fix allocation of temporary buffers
- Fix pitch computation
- Fix shadow plane allocation
tegra:
- use fbdev DMA helpers
- Convert to devm_platform_ioremap_resource()
- support bridge/connector
- enable PM
tidss:
- Support TI AM625 plus DT bindings
- Implement new connector model plus driver updates
vkms:
- improve write back support
- docs fixes
- support gamma LUT
zynqmp-dpsub:
- misc fixes"
* tag 'drm-next-2023-08-30' of git://anongit.freedesktop.org/drm/drm: (1327 commits)
drm/gpuva_mgr: remove unused prev pointer in __drm_gpuva_sm_map()
drm/tests/drm_kunit_helpers: Place correct function name in the comment header
drm/nouveau: uapi: don't pass NO_PREFETCH flag implicitly
drm/nouveau: uvmm: fix unset region pointer on remap
drm/nouveau: sched: avoid job races between entities
drm/i915: Fix HPD polling, reenabling the output poll work as needed
drm: Add an HPD poll helper to reschedule the poll work
drm/i915: Fix TLB-Invalidation seqno store
drm/ttm/tests: Fix type conversion in ttm_pool_test
drm/msm/a6xx: Bail out early if setting GPU OOB fails
drm/msm/a6xx: Move LLC accessors to the common header
drm/msm/a6xx: Introduce a6xx_llc_read
drm/ttm/tests: Require MMU when testing
drm/panel: simple: Fix Innolux G156HCE-L01 LVDS clock
Revert "Revert "drm/amdgpu/display: change pipe policy for DCN 2.0""
drm/amdgpu: Add memory vendor information
drm/amd: flush any delayed gfxoff on suspend entry
drm/amdgpu: skip fence GFX interrupts disable/enable for S0ix
drm/amdgpu: Remove gfxoff check in GFX v9.4.3
drm/amd/pm: Update pci link speed for smu v13.0.6
...
When no custom lock is set to protect a GEMs GPUVA list, lockdep checks
should fall back to the GEM objects dma-resv lock. With the current
implementation we're setting the lock_dep_map of the GEM objects 'resv'
pointer (in case no custom lock_dep_map is set yet) on
drm_gem_private_object_init().
However, the GEM objects 'resv' pointer might still change after
drm_gem_private_object_init() is called, e.g. through
ttm_bo_init_reserved(). This can result in the wrong lock being tracked.
To fix this, call dma_resv_held() directly from
drm_gem_gpuva_assert_lock_held() and fall back to the GEMs lock_dep_map
pointer only if an actual custom lock is set.
Fixes: e6303f323b ("drm: manager to keep track of GPUs VA mappings")
Reviewed-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Danilo Krummrich <dakr@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230804182406.5222-2-dakr@redhat.com
DRM bridges are not visible to the userspace and it may not be
immediately clear if the chain is somehow constructed incorrectly. I
have had two separate instances of a bridge driver failing to do a
drm_bridge_attach() call, resulting in the bridge connector not being
part of the chain. In some situations this doesn't seem to cause issues,
but it will if DRM_BRIDGE_ATTACH_NO_CONNECTOR flag is used.
Add a debugfs file to print the bridge chains. For me, on this TI AM62
based platform, I get the following output:
encoder[39]
bridge[0] type: 0, ops: 0x0
bridge[1] type: 0, ops: 0x0, OF: /bus@f0000/i2c@20000000/dsi@e:toshiba,tc358778
bridge[2] type: 0, ops: 0x3, OF: /bus@f0000/i2c@20010000/hdmi@48:lontium,lt8912b
bridge[3] type: 11, ops: 0x7, OF: /hdmi-connector:hdmi-connector
Tested-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Acked-by: Neil Armstrong <neil.armstrong@linaro.org>
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230802-drm-bridge-chain-debugfs-v4-1-7e3ae3d137c0@ideasonboard.com
These days, it's fairly common to see panels that have touchscreens
attached to them. The panel and the touchscreen can somewhat be
thought of as totally separate devices and, historically, this is how
Linux has treated them. However, treating them as separate isn't
necessarily the best way to model the two devices, it was just that
there was no better way. Specifically, there is little practical
reason to have the touchscreen powered on when the panel is turned
off, but if we model the devices separately we have no way to keep the
two devices' power states in sync with each other.
The issue described above makes it sound as if the problem here is
just about efficiency. We're wasting power keeping the touchscreen
powered up when the screen is off. While that's true, the problem can
go deeper. Specifically, hardware designers see that there's no reason
to have the touchscreen on while the screen is off and then build
hardware assuming that software would never turn the touchscreen on
while the screen is off.
In the very simplest case of hardware designs like this, the
touchscreen and the panel share some power rails. In most cases, this
turns out not to be terrible and is, again, just a little less
efficient. Specifically if we tell Linux that the touchscreen and the
panel are using the same rails then Linux will keep the rails on when
_either_ device is turned on. That ends to work OK-ish, but now if you
turn the panel off not only will the touchscreen remain powered, but
the power rails for the panel itself won't be switched off, burning
extra power.
The above two inefficiencies are _extra_ minor when you consider the
fact that laptops rarely spend much time with the screen off. The main
use case would be when an external screen (and presumably a power
supply) is attached.
Unfortunately, it gets worse from here. On sc7180-trogdor-homestar,
for instance, the display's TCON (timing controller) sometimes crashes
if you don't power cycle it whenever you stop and restart the video
stream (like during a modeset). The touchscreen keeping the power
rails on causes real problems. One proposal in the homestar timeframe
was to move the touchscreen to an always-on rail, dedicating the main
power rail to the panel. That caused _different_ problems as talked
about in commit 557e05fa9f ("HID: i2c-hid: goodix: Stop tying the
reset line to the regulator"). The end result of all of this was to
add an extra regulator to the board, increasing cost.
Recently, Cong Yang posted a patch [1] where things are even worse.
The panel and touch controller on that system seem even more
intimately tied together and really can't be thought of separately.
To address this issue, let's start allowing devices to register
themselves as "panel followers". These devices will get called after a
panel has been powered on and before a panel is powered off. This
makes the panel the primary device in charge of the power state, which
matches how userspace uses it.
The panel follower API should be fairly straightforward to use. The
current code assumes that panel followers are using device tree and
have a "panel" property pointing to the panel to follow. More
flexibility and non-DT implementations could be added as needed.
Right now, panel followers can follow the prepare/unprepare functions.
There could be arguments made that, instead, they should follow
enable/disable. I've chosen prepare/unprepare for now since those
functions are guaranteed to power up/power down the panel and it seems
better to start the process earlier.
A bit of explaining about why this is a roll-your-own API instead of
using something more standard:
1. In standard APIs in Linux, parent devices are automatically powered
on when a child needs power. Applying that here, it would mean that
we'd force the panel on any time someone was listening to the
touchscreen. That, unfortunately, would have broken homestar's need
(if we hadn't changed the hardware, as per above) where the panel
absolutely needs to be able to power cycle itself. While one could
argue that homestar is broken hardware and we shouldn't have the
API do backflips for it, _officially_ the eDP timing guidelines
agree with homestar's needs and the panel power sequencing diagrams
show power going off. It's nice to be able to support this.
2. We could, conceibably, try to add a new flag to device_link causing
the parent to be in charge of power. Then we could at least use
normal pm_runtime APIs. This sounds great, except that we run into
problems with initial probe. As talked about in the later patch
("HID: i2c-hid: Support being a panel follower") the initial power
on of a panel follower might need to do things (like add
sub-devices) that aren't allowed in a runtime_resume function.
The above complexities explain why this API isn't using common
functions. That being said, this patch is very small and
self-contained, so if someone was later able to adapt it to using more
common APIs while solving the above issues then that could happen in
the future.
[1] https://lore.kernel.org/r/20230519032316.3464732-1-yangcong5@huaqin.corp-partner.google.com
Reviewed-by: Maxime Ripard <mripard@kernel.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230727101636.v4.3.Icd5f96342d2242051c754364f4bee13ef2b986d4@changeid
In a whole pile of panel drivers, we have code to make the
prepare/unprepare/enable/disable callbacks behave as no-ops if they've
already been called. It's silly to have this code duplicated
everywhere. Add it to the core instead so that we can eventually
delete it from all the drivers. Note: to get some idea of the
duplicated code, try:
git grep 'if.*>prepared' -- drivers/gpu/drm/panel
git grep 'if.*>enabled' -- drivers/gpu/drm/panel
NOTE: arguably, the right thing to do here is actually to skip this
patch and simply remove all the extra checks from the individual
drivers. Perhaps the checks were needed at some point in time in the
past but maybe they no longer are? Certainly as we continue
transitioning over to "panel_bridge" then we expect there to be much
less variety in how these calls are made. When we're called as part of
the bridge chain, things should be pretty simple. In fact, there was
some discussion in the past about these checks [1], including a
discussion about whether the checks were needed and whether the calls
ought to be refcounted. At the time, I decided not to mess with it
because it felt too risky.
Looking closer at it now, I'm fairly certain that nothing in the
existing codebase is expecting these calls to be refcounted. The only
real question is whether someone is already doing something to ensure
prepare()/unprepare() match and enabled()/disable() match. I would say
that, even if there is something else ensuring that things match,
there's enough complexity that adding an extra bool and an extra
double-check here is a good idea. Let's add a drm_warn() to let people
know that it's considered a minor error to take advantage of
drm_panel's double-checking but we'll still make things work fine.
We'll also add an entry to the official DRM todo list to remove the
now pointless check from the panels after this patch lands and,
eventually, fixup anyone who is triggering the new warning.
[1] https://lore.kernel.org/r/20210416153909.v4.27.I502f2a92ddd36c3d28d014dd75e170c2d405a0a5@changeid
Acked-by: Neil Armstrong <neil.armstrong@linaro.org>
Reviewed-by: Maxime Ripard <mripard@kernel.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230727101636.v4.2.I59b417d4c29151cc2eff053369ec4822b606f375@changeid
