[PATCHv2 1/1] ARM: improve Cortex A8/A9 errata help text

[PATCHv2 1/1] ARM: improve Cortex A8/A9 errata help text

[Sebastian Reichel]

Docuemnt that !ARCH_MULTIPLATFORM is necessary because accessing
the the errata workaround registers may not work in non-secure
mode and mention that these erratas should be applied by the
bootloader instead.

Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>
---
Changes since RFCv1
 * https://lore.kernel.org/all/20221209182000.549179-1-sebastian.reichel@collabora.com/
 * update help text instead of removing !ARCH_MULTIPLATFORM
---
 arch/arm/Kconfig | 26 +++++++++++++++++++++-----
 1 file changed, 21 insertions(+), 5 deletions(-)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index a08c9d092a33..f81426422df4 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -656,7 +656,9 @@ config ARM_ERRATA_458693
 	  hazard might then cause a processor deadlock. The workaround enables
 	  the L1 caching of the NEON accesses and disables the PLD instruction
 	  in the ACTLR register. Note that setting specific bits in the ACTLR
-	  register may not be available in non-secure mode.
+	  register may not be available in non-secure mode and thus is not
+	  available on a multiplatform kernel. This should be applied by the
+	  bootloader instead.
 
 config ARM_ERRATA_460075
 	bool "ARM errata: Data written to the L2 cache can be overwritten with stale data"
@@ -669,7 +671,9 @@ config ARM_ERRATA_460075
 	  and overwritten with stale memory contents from external memory. The
 	  workaround disables the write-allocate mode for the L2 cache via the
 	  ACTLR register. Note that setting specific bits in the ACTLR register
-	  may not be available in non-secure mode.
+	  may not be available in non-secure mode and thus is not available on
+	  a multiplatform kernel. This should be applied by the bootloader
+	  instead.
 
 config ARM_ERRATA_742230
 	bool "ARM errata: DMB operation may be faulty"
@@ -682,7 +686,10 @@ config ARM_ERRATA_742230
 	  ordering of the two writes. This workaround sets a specific bit in
 	  the diagnostic register of the Cortex-A9 which causes the DMB
 	  instruction to behave as a DSB, ensuring the correct behaviour of
-	  the two writes.
+	  the two writes. Note that setting specific bits in the diagnostics
+	  register may not be available in non-secure mode and thus is not
+	  available on a multiplatform kernel. This should be applied by the
+	  bootloader instead.
 
 config ARM_ERRATA_742231
 	bool "ARM errata: Incorrect hazard handling in the SCU may lead to data corruption"
@@ -697,7 +704,10 @@ config ARM_ERRATA_742231
 	  replaced from one of the CPUs at the same time as another CPU is
 	  accessing it. This workaround sets specific bits in the diagnostic
 	  register of the Cortex-A9 which reduces the linefill issuing
-	  capabilities of the processor.
+	  capabilities of the processor. Note that setting specific bits in the
+	  diagnostics register may not be available in non-secure mode and thus
+	  is not available on a multiplatform kernel. This should be applied by
+	  the bootloader instead.
 
 config ARM_ERRATA_643719
 	bool "ARM errata: LoUIS bit field in CLIDR register is incorrect"
@@ -734,7 +744,9 @@ config ARM_ERRATA_743622
 	  register of the Cortex-A9 which disables the Store Buffer
 	  optimisation, preventing the defect from occurring. This has no
 	  visible impact on the overall performance or power consumption of the
-	  processor.
+	  processor. Note that setting specific bits in the diagnostics register
+	  may not be available in non-secure mode and thus is not available on a
+	  multiplatform kernel. This should be applied by the bootloader instead.
 
 config ARM_ERRATA_751472
 	bool "ARM errata: Interrupted ICIALLUIS may prevent completion of broadcasted operation"
@@ -746,6 +758,10 @@ config ARM_ERRATA_751472
 	  completion of a following broadcasted operation if the second
 	  operation is received by a CPU before the ICIALLUIS has completed,
 	  potentially leading to corrupted entries in the cache or TLB.
+	  Note that setting specific bits in the diagnostics register may
+	  not be available in non-secure mode and thus is not available on
+	  a multiplatform kernel. This should be applied by the bootloader
+	  instead.
 
 config ARM_ERRATA_754322
 	bool "ARM errata: possible faulty MMU translations following an ASID switch"
-- 
2.39.0

Re: [PATCHv2 1/1] ARM: improve Cortex A8/A9 errata help text

[AngeloGioacchino Del Regno]

Il 14/12/22 18:53, Sebastian Reichel ha scritto:
> Docuemnt that !ARCH_MULTIPLATFORM is necessary because accessing
> the the errata workaround registers may not work in non-secure
> mode and mention that these erratas should be applied by the
> bootloader instead.
> 
> Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

Followed the discussion... adding this information makes a lot of sense
and it's definitely helpful for developers (especially when some platform
encounters *strange* issues..)

So,

Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>

Cheers!

Re: [PATCHv2 1/1] ARM: improve Cortex A8/A9 errata help text

[Arnd Bergmann]

On Wed, Dec 14, 2022, at 18:53, Sebastian Reichel wrote:
> Docuemnt that !ARCH_MULTIPLATFORM is necessary because accessing
> the the errata workaround registers may not work in non-secure
> mode and mention that these erratas should be applied by the
> bootloader instead.
>
> Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

Reviewed-by: Arnd Bergmann <arnd@arndb.de>

Can you add this to Russell's patch tracker?

   Arnd

Re: [PATCHv2 1/1] ARM: improve Cortex A8/A9 errata help text

[Sebastian Reichel]

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Hi,

On Thu, Dec 15, 2022 at 02:58:43PM +0100, Arnd Bergmann wrote:
> On Wed, Dec 14, 2022, at 18:53, Sebastian Reichel wrote:
> > Docuemnt that !ARCH_MULTIPLATFORM is necessary because accessing
> > the the errata workaround registers may not work in non-secure
> > mode and mention that these erratas should be applied by the
> > bootloader instead.
> >
> > Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>
> 
> Reviewed-by: Arnd Bergmann <arnd@arndb.de>
> 
> Can you add this to Russell's patch tracker?

https://www.armlinux.org.uk/developer/patches/viewpatch.php?id=9281/1

-- Sebastian

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