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tty: hvc: restrict HVC_DCC to ARMv6+ and ARM64

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hvc_dcc drives the JTAG DCC via the ARMv6/v7 CP14 debug registers
(mrc/mcr p14, 0, rX, c0, c1/c5, 0 in asm/dcc.h). That encoding is
undefined on older ARM cores, and also on ARMv7-M, but HVC_DCC only
depends on ARM, so it can be enabled on e.g. ARM926 (ARCH_MULTI_V5),
where hvc_dcc_console_init() runs __dcc_putchar() at boot and takes an
undefined-instruction trap before the console is up:

  Internal error: Oops - undefined instruction: 0 [#1] ARM
  PC is at hvc_dcc_check+0x50/0x8c
   hvc_dcc_check from hvc_dcc_console_init+0x18/0x48
   hvc_dcc_console_init from console_init+0x58/0x170
  Kernel panic - not syncing: Fatal exception

Restrict HVC_DCC to the CPUs where that encoding is valid: the
CPU_V6 || CPU_V6K || CPU_V7 set that arch/arm/include/debug/icedcc.S
guards it with, plus ARM64.

Fixes: 16c63f8ea4 ("drivers: char: hvc: add arm JTAG DCC console support")
Signed-off-by: Karl Mehltretter <kmehltretter@gmail.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Link: https://patch.msgid.link/20260717071616.91423-1-kmehltretter@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Karl Mehltretter
2026-07-17 13:03:42 +02:00
committed by Greg Kroah-Hartman
parent a5ef89f7a8
commit 782f4dbd17
1 changed files with 1 additions and 1 deletions
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drivers/tty/hvc/Kconfig
+1 -1
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@@ -79,7 +79,7 @@ config HVC_UDBG
config HVC_DCC
bool "ARM JTAG DCC console"
depends on ARM || ARM64
depends on (ARM && (CPU_V6 || CPU_V6K || CPU_V7)) || ARM64
select HVC_DRIVER
select SERIAL_CORE_CONSOLE
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