Commit Graph

4503 Commits

Author SHA1 Message Date
Linus Torvalds 0ad5b053d4 Merge tag 'char-misc-5.7-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc
Pull char/misc driver updates from Greg KH:
 "Here is the big set of char/misc/other driver patches for 5.7-rc1.

  Lots of things in here, and it's later than expected due to some
  reverts to resolve some reported issues. All is now clean with no
  reported problems in linux-next.

  Included in here is:
   - interconnect updates
   - mei driver updates
   - uio updates
   - nvmem driver updates
   - soundwire updates
   - binderfs updates
   - coresight updates
   - habanalabs updates
   - mhi new bus type and core
   - extcon driver updates
   - some Kconfig cleanups
   - other small misc driver cleanups and updates

  As mentioned, all have been in linux-next for a while, and with the
  last two reverts, all is calm and good"

* tag 'char-misc-5.7-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc: (174 commits)
  Revert "driver core: platform: Initialize dma_parms for platform devices"
  Revert "amba: Initialize dma_parms for amba devices"
  amba: Initialize dma_parms for amba devices
  driver core: platform: Initialize dma_parms for platform devices
  bus: mhi: core: Drop the references to mhi_dev in mhi_destroy_device()
  bus: mhi: core: Initialize bhie field in mhi_cntrl for RDDM capture
  bus: mhi: core: Add support for reading MHI info from device
  misc: rtsx: set correct pcr_ops for rts522A
  speakup: misc: Use dynamic minor numbers for speakup devices
  mei: me: add cedar fork device ids
  coresight: do not use the BIT() macro in the UAPI header
  Documentation: provide IBM contacts for embargoed hardware
  nvmem: core: remove nvmem_sysfs_get_groups()
  nvmem: core: use is_bin_visible for permissions
  nvmem: core: use device_register and device_unregister
  nvmem: core: add root_only member to nvmem device struct
  extcon: axp288: Add wakeup support
  extcon: Mark extcon_get_edev_name() function as exported symbol
  extcon: palmas: Hide error messages if gpio returns -EPROBE_DEFER
  dt-bindings: extcon: usbc-cros-ec: convert extcon-usbc-cros-ec.txt to yaml format
  ...
2020-04-03 13:22:40 -07:00
Linus Torvalds 1f944f976d Merge tag 'tty-5.7-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty
Pull tty/serial updates from Greg KH:
 "Here is the big set of TTY / Serial patches for 5.7-rc1

  Lots of console fixups and reworking in here, serial core tweaks
  (doesn't that ever get old, why are we still creating new serial
  devices?), serial driver updates, line-protocol driver updates, and
  some vt cleanups and fixes included in here as well.

  All have been in linux-next with no reported issues"

* tag 'tty-5.7-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty: (161 commits)
  serial: 8250: Optimize irq enable after console write
  serial: 8250: Fix rs485 delay after console write
  vt: vt_ioctl: fix use-after-free in vt_in_use()
  vt: vt_ioctl: fix VT_DISALLOCATE freeing in-use virtual console
  tty: serial: make SERIAL_SPRD depend on COMMON_CLK
  tty: serial: fsl_lpuart: fix return value checking
  tty: serial: fsl_lpuart: move dma_request_chan()
  ARM: dts: tango4: Make /serial compatible with ns16550a
  ARM: dts: mmp*: Make the serial ports compatible with xscale-uart
  ARM: dts: mmp*: Fix serial port names
  ARM: dts: mmp2-brownstone: Don't redeclare phandle references
  ARM: dts: pxa*: Make the serial ports compatible with xscale-uart
  ARM: dts: pxa*: Fix serial port names
  ARM: dts: pxa*: Don't redeclare phandle references
  serial: omap: drop unused dt-bindings header
  serial: 8250: 8250_omap: Add DMA support for UARTs on K3 SoCs
  serial: 8250: 8250_omap: Work around errata causing spurious IRQs with DMA
  serial: 8250: 8250_omap: Extend driver data to pass FIFO trigger info
  serial: 8250: 8250_omap: Move locking out from __dma_rx_do_complete()
  serial: 8250: 8250_omap: Account for data in flight during DMA teardown
  ...
2020-03-31 16:18:55 -07:00
Rafael J. Wysocki 8f1073ed8c Merge branch 'pm-qos'
* pm-qos: (30 commits)
  PM: QoS: annotate data races in pm_qos_*_value()
  Documentation: power: fix pm_qos_interface.rst format warning
  PM: QoS: Make CPU latency QoS depend on CONFIG_CPU_IDLE
  Documentation: PM: QoS: Update to reflect previous code changes
  PM: QoS: Update file information comments
  PM: QoS: Drop PM_QOS_CPU_DMA_LATENCY and rename related functions
  sound: Call cpu_latency_qos_*() instead of pm_qos_*()
  drivers: usb: Call cpu_latency_qos_*() instead of pm_qos_*()
  drivers: tty: Call cpu_latency_qos_*() instead of pm_qos_*()
  drivers: spi: Call cpu_latency_qos_*() instead of pm_qos_*()
  drivers: net: Call cpu_latency_qos_*() instead of pm_qos_*()
  drivers: mmc: Call cpu_latency_qos_*() instead of pm_qos_*()
  drivers: media: Call cpu_latency_qos_*() instead of pm_qos_*()
  drivers: hsi: Call cpu_latency_qos_*() instead of pm_qos_*()
  drm: i915: Call cpu_latency_qos_*() instead of pm_qos_*()
  x86: platform: iosf_mbi: Call cpu_latency_qos_*() instead of pm_qos_*()
  cpuidle: Call cpu_latency_qos_limit() instead of pm_qos_request()
  PM: QoS: Add CPU latency QoS API wrappers
  PM: QoS: Adjust pm_qos_request() signature and reorder pm_qos.h
  PM: QoS: Simplify definitions of CPU latency QoS trace events
  ...
2020-03-30 14:45:57 +02:00
Lukas Wunner 8d5b305484 serial: 8250: Optimize irq enable after console write
Commit 7f9803072f ("serial: 8250: Support console on software emulated
rs485 ports") amended serial8250_console_write() with rs485 support, but
positioned the invocation of ->rs485_stop_tx() after re-enablement of
interrupts.  The irq handler and ->console_write() are serialized with
the port spinlock, so no problem there, but due to the rs485 delay, the
irq handler may unnecessarily spin for a while.  Avoid that by moving
->rs485_stop_tx() before re-enablement of interrupts, which also mirrors
the order at the beginning of serial8250_console_write().

Signed-off-by: Lukas Wunner <lukas@wunner.de>
Link: https://lore.kernel.org/r/019839cb1f61b01210b6ff9ac9f9079ca77f8411.1585319447.git.lukas@wunner.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2020-03-27 15:45:54 +01:00
Lukas Wunner 4e36f94e99 serial: 8250: Fix rs485 delay after console write
Due to a silly copy-paste mistake, commit 7f9803072f ("serial: 8250:
Support console on software emulated rs485 ports") erroneously pauses
for the duration of delay_rts_before_send after writing to the console,
instead of delay_rts_after_send.  Mea culpa.

Fixes: 7f9803072f ("serial: 8250: Support console on software emulated rs485 ports")
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Link: https://lore.kernel.org/r/9dd67f33c90d23f7fafa3b81b1e812ddabf9ca24.1585319447.git.lukas@wunner.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2020-03-27 15:45:54 +01:00
Chunyan Zhang 3b9c55efb2 tty: serial: make SERIAL_SPRD depend on COMMON_CLK
kbuild-test reported an error:

  config: mips-randconfig-a001-20200321 ...
  >> drivers/tty/serial/sprd_serial.c:1175: undefined reference
  to `clk_set_parent'

Because some mips Kconfig selects HAVE_CLK but not COMMON_CLK and no
clk_set_parent implemented, so the error was exposed. So adding
dependence on COMMON_CLK can fix this issue.

Fixes: 7ba87cfec7 ("tty: serial: make SERIAL_SPRD not depend on ARCH_SPRD")
Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Chunyan Zhang <chunyan.zhang@unisoc.com>
Link: https://lore.kernel.org/r/20200325081427.20312-1-zhang.lyra@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2020-03-26 15:41:03 +01:00
Michael Walle d7c53fb081 tty: serial: fsl_lpuart: fix return value checking
The return value of lpuart_dma_tx_request() is an negative errno on
failure and zero on success.

Fixes: 159381df14 ("tty: serial: fsl_lpuart: fix DMA operation when using IOMMU")
Reported-by: Leonard Crestez <leonard.crestez@nxp.com>
Signed-off-by: Michael Walle <michael@walle.cc>
Reviewed-by: Fugang Duan <fugang.duan@nxp.com>
Link: https://lore.kernel.org/r/20200325090658.25967-2-michael@walle.cc
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2020-03-26 15:34:05 +01:00
Michael Walle d0e7600b91 tty: serial: fsl_lpuart: move dma_request_chan()
Move dma_request_chan() out of the atomic context. First this call
should not be in the atomic context at all and second the
dev_info_once() may cause a hang because because the console takes this
spinlock, too.

Fixes: 159381df14 ("tty: serial: fsl_lpuart: fix DMA operation when using IOMMU")
Reported-by: Leonard Crestez <leonard.crestez@nxp.com>
Signed-off-by: Michael Walle <michael@walle.cc>
Reviewed-by: Fugang Duan <fugang.duan@nxp.com>
Tested-by: Leonard Crestez <leonard.crestez@nxp.com>
Link: https://lore.kernel.org/r/20200325090658.25967-1-michael@walle.cc
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2020-03-26 15:34:05 +01:00
Uwe Kleine-König c97c65f36e serial: omap: drop unused dt-bindings header
The definitons in the dt-binding's gpio header only contains some
constants to be used in device trees. It is not relevant for omap-serial
(as the gpio API hides the details) and in fact unused so it can just be
dropped.

Signed-off-by: Uwe Kleine-König <uwe@kleine-koenig.org>
Link: https://lore.kernel.org/r/20200321204031.30369-1-uwe@kleine-koenig.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2020-03-24 12:26:11 +01:00
Vignesh Raghavendra c26389f998 serial: 8250: 8250_omap: Add DMA support for UARTs on K3 SoCs
UART on K3 SoCs has configurable RX timeout behavior (controlled via
EFR2) and better DMA integration. This allows to transfer as larger
amount data per DMA transfer compared to older SoCs.  Add support for
the same.

Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Link: https://lore.kernel.org/r/20200319110344.21348-7-vigneshr@ti.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2020-03-24 12:25:11 +01:00
Vignesh Raghavendra c6689dfd87 serial: 8250: 8250_omap: Work around errata causing spurious IRQs with DMA
As per Advisory 27 of AM437x Silicon errata document, Spurious UART
interrupts may occur when DMA mode (FCR.DMA_MODE) is enabled. The
Interrupt Controller flags that a UART interrupt has occurred; however,
the associated IT_PENDING bit remains set to 1, indicating that no
interrupt is pending. Acknowledge the spurious interrupts for every
occurrence as workaround.

Errata is applicable to all TI SoCs with this IP.

Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Link: https://lore.kernel.org/r/20200319110344.21348-6-vigneshr@ti.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2020-03-24 12:25:11 +01:00
Vignesh Raghavendra 7229b84c20 serial: 8250: 8250_omap: Extend driver data to pass FIFO trigger info
Although same 8250 compliant UART IP is reused across different SoC,
their integration wrt DMA varies greatly across SoCs. Therefore,
different SoC may need to use different FIFO trigger level for DMA
event and DMA configuration parameters. Provide a way to pass this
information via driver data. This is required to support UART DMA on
AM654/J721e SoCs.

Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Link: https://lore.kernel.org/r/20200319110344.21348-5-vigneshr@ti.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2020-03-24 12:25:10 +01:00
Peter Ujfalusi 7898984167 serial: 8250: 8250_omap: Move locking out from __dma_rx_do_complete()
Caller functions of __dma_rx_do_complete() already hold rx_dma_lock.
Therefore move locking out of the function to avoid need to release and
reacquire lock.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Link: https://lore.kernel.org/r/20200319110344.21348-4-vigneshr@ti.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2020-03-24 12:25:10 +01:00
Vignesh Raghavendra 4bcf59a5de serial: 8250: 8250_omap: Account for data in flight during DMA teardown
Take into account data stuck in DMA internal buffers before pushing data
to higher layer. dma_tx_state has "in_flight_bytes" member that provides
this information.

Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Link: https://lore.kernel.org/r/20200319110344.21348-3-vigneshr@ti.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2020-03-24 12:25:10 +01:00
Vignesh Raghavendra 7cf4df30a9 serial: 8250: 8250_omap: Terminate DMA before pushing data on RX timeout
Terminate and flush DMA internal buffers, before pushing RX data to
higher layer. Otherwise, this will lead to data corruption, as driver
would end up pushing stale buffer data to higher layer while actual data
is still stuck inside DMA hardware and has yet not arrived at the
memory.
While at that, replace deprecated dmaengine_terminate_all() with
dmaengine_terminate_async().

Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Link: https://lore.kernel.org/r/20200319110344.21348-2-vigneshr@ti.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2020-03-24 12:25:10 +01:00
Peter Ujfalusi 4ce35a3617 serial: 8250_omap: Fix sleeping function called from invalid context during probe
When booting j721e the following bug is printed:

[    1.154821] BUG: sleeping function called from invalid context at kernel/sched/completion.c:99
[    1.154827] in_atomic(): 0, irqs_disabled(): 128, non_block: 0, pid: 12, name: kworker/0:1
[    1.154832] 3 locks held by kworker/0:1/12:
[    1.154836]  #0: ffff000840030728 ((wq_completion)events){+.+.}, at: process_one_work+0x1d4/0x6e8
[    1.154852]  #1: ffff80001214fdd8 (deferred_probe_work){+.+.}, at: process_one_work+0x1d4/0x6e8
[    1.154860]  #2: ffff00084060b170 (&dev->mutex){....}, at: __device_attach+0x38/0x138
[    1.154872] irq event stamp: 63096
[    1.154881] hardirqs last  enabled at (63095): [<ffff800010b74318>] _raw_spin_unlock_irqrestore+0x70/0x78
[    1.154887] hardirqs last disabled at (63096): [<ffff800010b740d8>] _raw_spin_lock_irqsave+0x28/0x80
[    1.154893] softirqs last  enabled at (62254): [<ffff800010080c88>] _stext+0x488/0x564
[    1.154899] softirqs last disabled at (62247): [<ffff8000100fdb3c>] irq_exit+0x114/0x140
[    1.154906] CPU: 0 PID: 12 Comm: kworker/0:1 Not tainted 5.6.0-rc6-next-20200318-00094-g45e4089b0bd3 #221
[    1.154911] Hardware name: Texas Instruments K3 J721E SoC (DT)
[    1.154917] Workqueue: events deferred_probe_work_func
[    1.154923] Call trace:
[    1.154928]  dump_backtrace+0x0/0x190
[    1.154933]  show_stack+0x14/0x20
[    1.154940]  dump_stack+0xe0/0x148
[    1.154946]  ___might_sleep+0x150/0x1f0
[    1.154952]  __might_sleep+0x4c/0x80
[    1.154957]  wait_for_completion_timeout+0x40/0x140
[    1.154964]  ti_sci_set_device_state+0xa0/0x158
[    1.154969]  ti_sci_cmd_get_device_exclusive+0x14/0x20
[    1.154977]  ti_sci_dev_start+0x34/0x50
[    1.154984]  genpd_runtime_resume+0x78/0x1f8
[    1.154991]  __rpm_callback+0x3c/0x140
[    1.154996]  rpm_callback+0x20/0x80
[    1.155001]  rpm_resume+0x568/0x758
[    1.155007]  __pm_runtime_resume+0x44/0xb0
[    1.155013]  omap8250_probe+0x2b4/0x508
[    1.155019]  platform_drv_probe+0x50/0xa0
[    1.155023]  really_probe+0xd4/0x318
[    1.155028]  driver_probe_device+0x54/0xe8
[    1.155033]  __device_attach_driver+0x80/0xb8
[    1.155039]  bus_for_each_drv+0x74/0xc0
[    1.155044]  __device_attach+0xdc/0x138
[    1.155049]  device_initial_probe+0x10/0x18
[    1.155053]  bus_probe_device+0x98/0xa0
[    1.155058]  deferred_probe_work_func+0x74/0xb0
[    1.155063]  process_one_work+0x280/0x6e8
[    1.155068]  worker_thread+0x48/0x430
[    1.155073]  kthread+0x108/0x138
[    1.155079]  ret_from_fork+0x10/0x18

To fix the bug we need to first call pm_runtime_enable() prior to any
pm_runtime calls.

Reported-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Link: https://lore.kernel.org/r/20200320125200.6772-1-peter.ujfalusi@ti.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2020-03-24 12:25:09 +01:00
Vignesh Raghavendra f4b042a050 serial: 8250: 8250_omap: Fix throttle to call stop_rx()
Call stop_rx() to halt reception when throttle is requested. Update
unthrottle callback to restart reception.

Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Link: https://lore.kernel.org/r/20200319103230.16867-3-vigneshr@ti.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2020-03-24 12:25:09 +01:00
Vignesh Raghavendra f19c3f6c81 serial: 8250_port: Don't service RX FIFO if throttled
When port's throttle callback is called, it should stop pushing any more
data into TTY buffer to avoid buffer overflow. This means driver has to
stop HW from receiving more data and assert the HW flow control. For
UARTs with auto HW flow control (such as 8250_omap) manual assertion of
flow control line is not possible and only way is to allow RX FIFO to
fill up, thus trigger auto HW flow control logic.

Therefore make sure that 8250 generic IRQ handler does not drain data
when port is stopped (i.e UART_LSR_DR is unset in read_status_mask). Not
servicing, RX FIFO would trigger auto HW flow control when FIFO
occupancy reaches preset threshold, thus halting RX.
Since, error conditions in UART_LSR register are cleared just by reading
the register, data has to be drained in case there are FIFO errors, else
error information will lost.

Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Link: https://lore.kernel.org/r/20200319103230.16867-2-vigneshr@ti.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2020-03-24 12:25:09 +01:00
Raviteja Narayanam 706bbc572d serial: uartps: Add TACTIVE check in cdns_uart_tx_empty function
Make sure that all bytes are transmitted out of Uart by monitoring
CDNS_UART_SR_TACTIVE bit as well.

Signed-off-by: Raviteja Narayanam <raviteja.narayanam@xilinx.com>
Signed-off-by: Shubhrajyoti Datta <shubhrajyoti.datta@xilinx.com>
Acked-by: Maarten Brock <m.brock@vanmierlo.com>
Link: https://lore.kernel.org/r/e2514818af5973be291cc117d07739f068b71639.1584610774.git.shubhrajyoti.datta@xilinx.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2020-03-24 12:23:04 +01:00
Raviteja Narayanam 97451855cc serial: uartps: Remove unconditional wait inside set_termios
set_termios function should not wait for the transmit FIFO empty
(CDNS_UART_SR_TXEMPTY) unconditionally. The tty layer takes care
of it based on the parameter passed (TCSANOW/TCSADRAIN/TCSAFLUSH).

Signed-off-by: Raviteja Narayanam <raviteja.narayanam@xilinx.com>
Signed-off-by: Shubhrajyoti Datta <shubhrajyoti.datta@xilinx.com>
Link: https://lore.kernel.org/r/536e190dd5bbb474007a67e6323c048288942a28.1584610774.git.shubhrajyoti.datta@xilinx.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2020-03-24 12:23:03 +01:00
Takashi Iwai e39c0ffe8c tty: serial: pch_uart: Use scnprintf() for avoiding potential buffer overflow
Since snprintf() returns the would-be-output size instead of the
actual output size, the succeeding calls may go beyond the given
buffer limit.  Fix it by replacing with scnprintf().

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Link: https://lore.kernel.org/r/20200311092930.24433-1-tiwai@suse.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2020-03-18 12:59:29 +01:00
Chunyan Zhang 7253407747 serial: sprd: remove redundant sprd_port cleanup
We don't need to cleanup sprd_port anymore, since we've dropped the way
of using the sprd_port[] array to get port index.

Reviewed-by: Baolin Wang <baolin.wang7@gmail.com>
Signed-off-by: Chunyan Zhang <chunyan.zhang@unisoc.com>
Link: https://lore.kernel.org/r/20200318105049.19623-3-zhang.lyra@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2020-03-18 12:20:04 +01:00
Chunyan Zhang 4b7349cb4e serial: sprd: getting port index via serial aliases only
This patch simplifies the process of getting serial port number, with
this patch, serial devices must have aliases configured in devicetree.

The serial port searched out via sprd_port array maybe wrong if we don't
have serial alias defined in devicetree, and specify console with command
line, we would get the wrong port number if other serial ports probe
failed before console's. So using aliases is mandatory.

Reviewed-by: Baolin Wang <baolin.wang7@gmail.com>
Signed-off-by: Chunyan Zhang <chunyan.zhang@unisoc.com>
Link: https://lore.kernel.org/r/20200318105049.19623-2-zhang.lyra@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2020-03-18 12:20:04 +01:00
Vincent Chen 630db5cbc7 tty: serial: Add CONSOLE_POLL support to SiFive UART
Add CONSOLE_POLL support for future KGDB porting.

Signed-off-by: Vincent Chen <vincent.chen@sifive.com>

Changes since v1:
1. Fix the compile error reported by kbuild test robot
Link: https://lore.kernel.org/r/1584492027-23236-1-git-send-email-vincent.chen@sifive.com

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2020-03-18 11:07:13 +01:00
Andy Shevchenko 089b6d3654 serial: 8250_port: Disable DMA operations for kernel console
It would be too tricky and error prone to allow DMA operations on
kernel console.

One of the concern is when DMA is a separate device, for example on
Intel CherryTrail platforms, and might need special work around to be
functional, see the commit

  eebb3e8d8a ("ACPI / LPSS: override power state for LPSS DMA device")

for more information.

Another one is that kernel console is used in atomic context, e.g.
when printing crucial information to the user (Oops or crash),
and DMA may not serve due to power management complications
including non-atomic ACPI calls but not limited to it (see above).

Besides that, other concerns are described in the commit

  84b40e3b57 ("serial: 8250: omap: Disable DMA for console UART")

done for OMAP UART and may be repeated here.

Disable any kind of DMA operations on kernel console due to above concerns.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20200217114016.49856-7-andriy.shevchenko@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2020-03-17 15:58:00 +01:00