[PATCH 1/3] arm64: Disable GiC priorities on Mediatek devices w/ firmware issues

[PATCH 1/3] arm64: Disable GiC priorities on Mediatek devices w/ firmware issues

[Douglas Anderson]

In commit 44bd78dd2b88 ("irqchip/gic-v3: Disable pseudo NMIs on
Mediatek devices w/ firmware issues") we added a method for detecting
Mediatek devices with broken firmware and disabled pseudo-NMI. While
that worked, it didn't address the problem at a deep enough level.

The fundamental issue with this broken firmware is that it's not
saving and restoring several important GICR registers. The current
list is believed to be:
* GICR_NUM_IPRIORITYR
* GICR_CTLR
* GICR_ISPENDR0
* GICR_ISACTIVER0
* GICR_NSACR

Pseudo-NMI didn't work because it was the only thing (currently) in
the kernel that relied on the broken registers, so forcing pseudo-NMI
off was an effective fix. However, it could be observed that calling
system_uses_irq_prio_masking() on these systems still returned
"true". That caused confusion and led to the need for
commit a07a59415217 ("arm64: smp: avoid NMI IPIs with broken MediaTek
FW"). It's worried that the incorrect value returned by
system_uses_irq_prio_masking() on these systems will continue to
confuse future developers.

Let's fix the issue a little more completely by disabling IRQ
priorities at a deeper level in the kernel. Once we do this we can
revert some of the other bits of code dealing with this quirk.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
---

 arch/arm64/kernel/cpufeature.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 2806a2850e78..e35efab8efa9 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -2094,9 +2094,30 @@ static int __init early_enable_pseudo_nmi(char *p)
 }
 early_param("irqchip.gicv3_pseudo_nmi", early_enable_pseudo_nmi);
 
+static bool are_gic_priorities_broken(void)
+{
+	bool is_broken = false;
+	struct device_node *np;
+
+	/*
+	 * Detect broken Mediatek firmware that doesn't properly save and
+	 * restore GIC priorities.
+	 */
+	np = of_find_compatible_node(NULL, NULL, "arm,gic-v3");
+	if (np) {
+		is_broken = of_property_read_bool(np, "mediatek,broken-save-restore-fw");
+		of_node_put(np);
+	}
+
+	return is_broken;
+}
+
 static bool can_use_gic_priorities(const struct arm64_cpu_capabilities *entry,
 				   int scope)
 {
+	if (are_gic_priorities_broken())
+		return false;
+
 	/*
 	 * ARM64_HAS_GIC_CPUIF_SYSREGS has a lower index, and is a boot CPU
 	 * feature, so will be detected earlier.
-- 
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[PATCH 2/3] Revert "arm64: smp: avoid NMI IPIs with broken MediaTek FW"

[Douglas Anderson]

This reverts commit a07a594152173a3dd3bdd12fc7d73dbba54cdbca.

This is no longer needed after the patch ("arm64: Disable GiC
priorities on Mediatek devices w/ firmware issues").

Signed-off-by: Douglas Anderson <dianders@chromium.org>
---

 arch/arm64/kernel/smp.c      | 5 +----
 drivers/irqchip/irq-gic-v3.c | 2 +-
 2 files changed, 2 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index 16ead57a583d..f36a97a54d2b 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -964,10 +964,7 @@ static void smp_cross_call(const struct cpumask *target, unsigned int ipinr)
 
 static bool ipi_should_be_nmi(enum ipi_msg_type ipi)
 {
-	DECLARE_STATIC_KEY_FALSE(supports_pseudo_nmis);
-
-	if (!system_uses_irq_prio_masking() ||
-	    !static_branch_likely(&supports_pseudo_nmis))
+	if (!system_uses_irq_prio_masking())
 		return false;
 
 	switch (ipi) {
diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
index 737da1b9aabf..787ccc880b22 100644
--- a/drivers/irqchip/irq-gic-v3.c
+++ b/drivers/irqchip/irq-gic-v3.c
@@ -106,7 +106,7 @@ static DEFINE_STATIC_KEY_TRUE(supports_deactivate_key);
  * - Figure 4-7 Secure read of the priority field for a Non-secure Group 1
  *   interrupt.
  */
-DEFINE_STATIC_KEY_FALSE(supports_pseudo_nmis);
+static DEFINE_STATIC_KEY_FALSE(supports_pseudo_nmis);
 
 DEFINE_STATIC_KEY_FALSE(gic_nonsecure_priorities);
 EXPORT_SYMBOL(gic_nonsecure_priorities);
-- 
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Re: [PATCH 2/3] Revert "arm64: smp: avoid NMI IPIs with broken MediaTek FW"

[Mark Rutland]

On Fri, Oct 06, 2023 at 03:15:52PM -0700, Douglas Anderson wrote:
> This reverts commit a07a594152173a3dd3bdd12fc7d73dbba54cdbca.
> 
> This is no longer needed after the patch ("arm64: Disable GiC
> priorities on Mediatek devices w/ firmware issues").

That first patch has a typo in the title: s/GiC/GIC/

This patch makes sense to me, so:

Acked-by: Mark Rutland <mark.rutland@arm.com>

Mark.

> 
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> ---
> 
>  arch/arm64/kernel/smp.c      | 5 +----
>  drivers/irqchip/irq-gic-v3.c | 2 +-
>  2 files changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
> index 16ead57a583d..f36a97a54d2b 100644
> --- a/arch/arm64/kernel/smp.c
> +++ b/arch/arm64/kernel/smp.c
> @@ -964,10 +964,7 @@ static void smp_cross_call(const struct cpumask *target, unsigned int ipinr)
>  
>  static bool ipi_should_be_nmi(enum ipi_msg_type ipi)
>  {
> -	DECLARE_STATIC_KEY_FALSE(supports_pseudo_nmis);
> -
> -	if (!system_uses_irq_prio_masking() ||
> -	    !static_branch_likely(&supports_pseudo_nmis))
> +	if (!system_uses_irq_prio_masking())
>  		return false;
>  
>  	switch (ipi) {
> diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
> index 737da1b9aabf..787ccc880b22 100644
> --- a/drivers/irqchip/irq-gic-v3.c
> +++ b/drivers/irqchip/irq-gic-v3.c
> @@ -106,7 +106,7 @@ static DEFINE_STATIC_KEY_TRUE(supports_deactivate_key);
>   * - Figure 4-7 Secure read of the priority field for a Non-secure Group 1
>   *   interrupt.
>   */
> -DEFINE_STATIC_KEY_FALSE(supports_pseudo_nmis);
> +static DEFINE_STATIC_KEY_FALSE(supports_pseudo_nmis);
>  
>  DEFINE_STATIC_KEY_FALSE(gic_nonsecure_priorities);
>  EXPORT_SYMBOL(gic_nonsecure_priorities);
> -- 
> 2.42.0.609.gbb76f46606-goog
> 

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[PATCH 3/3] irqchip/gic-v3: Remove Mediatek pseudo-NMI firmware quirk handling

[Douglas Anderson]

This is a partial revert of commit 44bd78dd2b88 ("irqchip/gic-v3:
Disable pseudo NMIs on Mediatek devices w/ firmware issues"). In the
patch ("arm64: Disable GiC priorities on Mediatek devices w/ firmware
issues") we've moved the quirk handling to another place and so it's
not needed in the GiC driver.

NOTE: this isn't a full revert because it leaves some of the changes
to the "quirks" structure around in case future code needs it.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
---

 drivers/irqchip/irq-gic-v3.c | 22 +---------------------
 1 file changed, 1 insertion(+), 21 deletions(-)

diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
index 787ccc880b22..9ff776709ae6 100644
--- a/drivers/irqchip/irq-gic-v3.c
+++ b/drivers/irqchip/irq-gic-v3.c
@@ -39,8 +39,7 @@
 
 #define FLAGS_WORKAROUND_GICR_WAKER_MSM8996	(1ULL << 0)
 #define FLAGS_WORKAROUND_CAVIUM_ERRATUM_38539	(1ULL << 1)
-#define FLAGS_WORKAROUND_MTK_GICR_SAVE		(1ULL << 2)
-#define FLAGS_WORKAROUND_ASR_ERRATUM_8601001	(1ULL << 3)
+#define FLAGS_WORKAROUND_ASR_ERRATUM_8601001	(1ULL << 2)
 
 #define GIC_IRQ_TYPE_PARTITION	(GIC_IRQ_TYPE_LPI + 1)
 
@@ -1790,15 +1789,6 @@ static bool gic_enable_quirk_msm8996(void *data)
 	return true;
 }
 
-static bool gic_enable_quirk_mtk_gicr(void *data)
-{
-	struct gic_chip_data *d = data;
-
-	d->flags |= FLAGS_WORKAROUND_MTK_GICR_SAVE;
-
-	return true;
-}
-
 static bool gic_enable_quirk_cavium_38539(void *data)
 {
 	struct gic_chip_data *d = data;
@@ -1891,11 +1881,6 @@ static const struct gic_quirk gic_quirks[] = {
 		.compatible = "asr,asr8601-gic-v3",
 		.init	= gic_enable_quirk_asr8601,
 	},
-	{
-		.desc	= "GICv3: Mediatek Chromebook GICR save problem",
-		.property = "mediatek,broken-save-restore-fw",
-		.init	= gic_enable_quirk_mtk_gicr,
-	},
 	{
 		.desc	= "GICv3: HIP06 erratum 161010803",
 		.iidr	= 0x0204043b,
@@ -1957,11 +1942,6 @@ static void gic_enable_nmi_support(void)
 	if (!gic_prio_masking_enabled())
 		return;
 
-	if (gic_data.flags & FLAGS_WORKAROUND_MTK_GICR_SAVE) {
-		pr_warn("Skipping NMI enable due to firmware issues\n");
-		return;
-	}
-
 	rdist_nmi_refs = kcalloc(gic_data.ppi_nr + SGI_NR,
 				 sizeof(*rdist_nmi_refs), GFP_KERNEL);
 	if (!rdist_nmi_refs)
-- 
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Re: [PATCH 3/3] irqchip/gic-v3: Remove Mediatek pseudo-NMI firmware quirk handling

[Mark Rutland]

On Fri, Oct 06, 2023 at 03:15:53PM -0700, Douglas Anderson wrote:
> This is a partial revert of commit 44bd78dd2b88 ("irqchip/gic-v3:
> Disable pseudo NMIs on Mediatek devices w/ firmware issues"). In the
> patch ("arm64: Disable GiC priorities on Mediatek devices w/ firmware
> issues") we've moved the quirk handling to another place and so it's
> not needed in the GiC driver.
> 
> NOTE: this isn't a full revert because it leaves some of the changes
> to the "quirks" structure around in case future code needs it.
> 
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> ---

I think it might make sense to fold this into the patch adding the cpucap
detection. Otherwise, if you apply my suggestions to the first patch, there's a
2-commit window where we'll have two places that log that NMI is being disabled
due to the FW issue. That's not a functional issue, so doesn't matter that
much.

Either way:

Acked-by: Mark Rutland <mark.rutland@arm.com>

Mark.

> 
>  drivers/irqchip/irq-gic-v3.c | 22 +---------------------
>  1 file changed, 1 insertion(+), 21 deletions(-)
> 
> diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
> index 787ccc880b22..9ff776709ae6 100644
> --- a/drivers/irqchip/irq-gic-v3.c
> +++ b/drivers/irqchip/irq-gic-v3.c
> @@ -39,8 +39,7 @@
>  
>  #define FLAGS_WORKAROUND_GICR_WAKER_MSM8996	(1ULL << 0)
>  #define FLAGS_WORKAROUND_CAVIUM_ERRATUM_38539	(1ULL << 1)
> -#define FLAGS_WORKAROUND_MTK_GICR_SAVE		(1ULL << 2)
> -#define FLAGS_WORKAROUND_ASR_ERRATUM_8601001	(1ULL << 3)
> +#define FLAGS_WORKAROUND_ASR_ERRATUM_8601001	(1ULL << 2)
>  
>  #define GIC_IRQ_TYPE_PARTITION	(GIC_IRQ_TYPE_LPI + 1)
>  
> @@ -1790,15 +1789,6 @@ static bool gic_enable_quirk_msm8996(void *data)
>  	return true;
>  }
>  
> -static bool gic_enable_quirk_mtk_gicr(void *data)
> -{
> -	struct gic_chip_data *d = data;
> -
> -	d->flags |= FLAGS_WORKAROUND_MTK_GICR_SAVE;
> -
> -	return true;
> -}
> -
>  static bool gic_enable_quirk_cavium_38539(void *data)
>  {
>  	struct gic_chip_data *d = data;
> @@ -1891,11 +1881,6 @@ static const struct gic_quirk gic_quirks[] = {
>  		.compatible = "asr,asr8601-gic-v3",
>  		.init	= gic_enable_quirk_asr8601,
>  	},
> -	{
> -		.desc	= "GICv3: Mediatek Chromebook GICR save problem",
> -		.property = "mediatek,broken-save-restore-fw",
> -		.init	= gic_enable_quirk_mtk_gicr,
> -	},
>  	{
>  		.desc	= "GICv3: HIP06 erratum 161010803",
>  		.iidr	= 0x0204043b,
> @@ -1957,11 +1942,6 @@ static void gic_enable_nmi_support(void)
>  	if (!gic_prio_masking_enabled())
>  		return;
>  
> -	if (gic_data.flags & FLAGS_WORKAROUND_MTK_GICR_SAVE) {
> -		pr_warn("Skipping NMI enable due to firmware issues\n");
> -		return;
> -	}
> -
>  	rdist_nmi_refs = kcalloc(gic_data.ppi_nr + SGI_NR,
>  				 sizeof(*rdist_nmi_refs), GFP_KERNEL);
>  	if (!rdist_nmi_refs)
> -- 
> 2.42.0.609.gbb76f46606-goog
> 

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Re: [PATCH 3/3] irqchip/gic-v3: Remove Mediatek pseudo-NMI firmware quirk handling

[Doug Anderson]

Hi,

On Wed, Oct 18, 2023 at 4:08 AM Mark Rutland <mark.rutland@arm.com> wrote:
>
> On Fri, Oct 06, 2023 at 03:15:53PM -0700, Douglas Anderson wrote:
> > This is a partial revert of commit 44bd78dd2b88 ("irqchip/gic-v3:
> > Disable pseudo NMIs on Mediatek devices w/ firmware issues"). In the
> > patch ("arm64: Disable GiC priorities on Mediatek devices w/ firmware
> > issues") we've moved the quirk handling to another place and so it's
> > not needed in the GiC driver.
> >
> > NOTE: this isn't a full revert because it leaves some of the changes
> > to the "quirks" structure around in case future code needs it.
> >
> > Signed-off-by: Douglas Anderson <dianders@chromium.org>
> > ---
>
> I think it might make sense to fold this into the patch adding the cpucap
> detection. Otherwise, if you apply my suggestions to the first patch, there's a
> 2-commit window where we'll have two places that log that NMI is being disabled
> due to the FW issue. That's not a functional issue, so doesn't matter that
> much.
>
> Either way:
>
> Acked-by: Mark Rutland <mark.rutland@arm.com>

I'm happy to go either way so I'd love some advice from maintainers
(Marc Zyngier, Catalin Marinas, Will Deacon) about what you'd prefer.

-Doug

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Re: [PATCH 3/3] irqchip/gic-v3: Remove Mediatek pseudo-NMI firmware quirk handling

[Marc Zyngier]

On 2023-10-30 23:01, Doug Anderson wrote:
> Hi,
> 
> On Wed, Oct 18, 2023 at 4:08 AM Mark Rutland <mark.rutland@arm.com> 
> wrote:
>> 
>> On Fri, Oct 06, 2023 at 03:15:53PM -0700, Douglas Anderson wrote:
>> > This is a partial revert of commit 44bd78dd2b88 ("irqchip/gic-v3:
>> > Disable pseudo NMIs on Mediatek devices w/ firmware issues"). In the
>> > patch ("arm64: Disable GiC priorities on Mediatek devices w/ firmware
>> > issues") we've moved the quirk handling to another place and so it's
>> > not needed in the GiC driver.
>> >
>> > NOTE: this isn't a full revert because it leaves some of the changes
>> > to the "quirks" structure around in case future code needs it.
>> >
>> > Signed-off-by: Douglas Anderson <dianders@chromium.org>
>> > ---
>> 
>> I think it might make sense to fold this into the patch adding the 
>> cpucap
>> detection. Otherwise, if you apply my suggestions to the first patch, 
>> there's a
>> 2-commit window where we'll have two places that log that NMI is being 
>> disabled
>> due to the FW issue. That's not a functional issue, so doesn't matter 
>> that
>> much.
>> 
>> Either way:
>> 
>> Acked-by: Mark Rutland <mark.rutland@arm.com>
> 
> I'm happy to go either way so I'd love some advice from maintainers
> (Marc Zyngier, Catalin Marinas, Will Deacon) about what you'd prefer.

I honestly don't mind either way. The sooner we have these fixes
upstream, the better, so my only advise would be to respin it
shortly.

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...

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Re: [PATCH 3/3] irqchip/gic-v3: Remove Mediatek pseudo-NMI firmware quirk handling

[Catalin Marinas]

On Tue, Nov 07, 2023 at 11:37:18AM +0000, Marc Zyngier wrote:
> On 2023-10-30 23:01, Doug Anderson wrote:
> > On Wed, Oct 18, 2023 at 4:08 AM Mark Rutland <mark.rutland@arm.com>
> > wrote:
> > > On Fri, Oct 06, 2023 at 03:15:53PM -0700, Douglas Anderson wrote:
> > > > This is a partial revert of commit 44bd78dd2b88 ("irqchip/gic-v3:
> > > > Disable pseudo NMIs on Mediatek devices w/ firmware issues"). In the
> > > > patch ("arm64: Disable GiC priorities on Mediatek devices w/ firmware
> > > > issues") we've moved the quirk handling to another place and so it's
> > > > not needed in the GiC driver.
> > > >
> > > > NOTE: this isn't a full revert because it leaves some of the changes
> > > > to the "quirks" structure around in case future code needs it.
> > > >
> > > > Signed-off-by: Douglas Anderson <dianders@chromium.org>
> > > > ---
> > > 
> > > I think it might make sense to fold this into the patch adding the
> > > cpucap
> > > detection. Otherwise, if you apply my suggestions to the first
> > > patch, there's a
> > > 2-commit window where we'll have two places that log that NMI is
> > > being disabled
> > > due to the FW issue. That's not a functional issue, so doesn't
> > > matter that
> > > much.
> > > 
> > > Either way:
> > > 
> > > Acked-by: Mark Rutland <mark.rutland@arm.com>
> > 
> > I'm happy to go either way so I'd love some advice from maintainers
> > (Marc Zyngier, Catalin Marinas, Will Deacon) about what you'd prefer.
> 
> I honestly don't mind either way. The sooner we have these fixes
> upstream, the better, so my only advise would be to respin it
> shortly.

I agree. I can queue them for rc1 if they turn up in time.

-- 
Catalin

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Re: [PATCH 1/3] arm64: Disable GiC priorities on Mediatek devices w/ firmware issues

[Mark Rutland]

On Fri, Oct 06, 2023 at 03:15:51PM -0700, Douglas Anderson wrote:
> In commit 44bd78dd2b88 ("irqchip/gic-v3: Disable pseudo NMIs on
> Mediatek devices w/ firmware issues") we added a method for detecting
> Mediatek devices with broken firmware and disabled pseudo-NMI. While
> that worked, it didn't address the problem at a deep enough level.
> 
> The fundamental issue with this broken firmware is that it's not
> saving and restoring several important GICR registers. The current
> list is believed to be:
> * GICR_NUM_IPRIORITYR
> * GICR_CTLR
> * GICR_ISPENDR0
> * GICR_ISACTIVER0
> * GICR_NSACR
> 
> Pseudo-NMI didn't work because it was the only thing (currently) in
> the kernel that relied on the broken registers, so forcing pseudo-NMI
> off was an effective fix. However, it could be observed that calling
> system_uses_irq_prio_masking() on these systems still returned
> "true". That caused confusion and led to the need for
> commit a07a59415217 ("arm64: smp: avoid NMI IPIs with broken MediaTek
> FW"). It's worried that the incorrect value returned by
> system_uses_irq_prio_masking() on these systems will continue to
> confuse future developers.
> 
> Let's fix the issue a little more completely by disabling IRQ
> priorities at a deeper level in the kernel. Once we do this we can
> revert some of the other bits of code dealing with this quirk.
> 
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> ---
> 
>  arch/arm64/kernel/cpufeature.c | 21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)
> 
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index 2806a2850e78..e35efab8efa9 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -2094,9 +2094,30 @@ static int __init early_enable_pseudo_nmi(char *p)
>  }
>  early_param("irqchip.gicv3_pseudo_nmi", early_enable_pseudo_nmi);
>  
> +static bool are_gic_priorities_broken(void)
> +{
> +	bool is_broken = false;
> +	struct device_node *np;
> +
> +	/*
> +	 * Detect broken Mediatek firmware that doesn't properly save and
> +	 * restore GIC priorities.
> +	 */
> +	np = of_find_compatible_node(NULL, NULL, "arm,gic-v3");
> +	if (np) {
> +		is_broken = of_property_read_bool(np, "mediatek,broken-save-restore-fw");
> +		of_node_put(np);
> +	}
> +
> +	return is_broken;
> +}

I'm definitely in favour of detecting this in the cpucap, but I think it'd be
better to parse the DT once on the boot CPU rather than on each CPU every time
it's brought up.

I think if we add something like:

#ifdef CONFIG_ARM64_PSEUDO_NMI
static void detect_system_supports_pseudo_nmi(void)
{
	struct device_node *np;

	if (!enable_pseudo_nmi)
		return;
	
	/*
	 * Detect broken Mediatek firmware that doesn't properly save and
	 * restore GIC priorities.
	 */
	np = of_find_compatible_node(NULL, NULL, "arm,gic-v3");
	if (np && of_property_read_bool(np, "mediatek,broken-save-restore-fw")) {
		pr_info("Pseudo-NMI disabled due to Mediatek Chromebook GICR save problem");
		enable_pseudo_nmi = false;
	}
	of_node_put(np);
}
#endif /* CONFIG_ARM64_PSEUDO_NMI */
static inline void detect_system_supports_pseudo_nmi(void) { }
#endif

... then we can call that from init_cpu_features() before we call
setup_boot_cpu_capabilities(), and then the existing logic in
can_use_gic_priorities() should just work as that returns the value of
enable_pseudo_nmi.

Note: of_node_put(NULL) does nothing, like kfree(NULL), so it's fine for that
to be called in the !np case.

Would you be happy to fold that in? I'm happy with a Suggested-by tag if so. :)

Mark

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Re: [PATCH 1/3] arm64: Disable GiC priorities on Mediatek devices w/ firmware issues

[Doug Anderson]

Hi,

On Wed, Oct 18, 2023 at 4:01 AM Mark Rutland <mark.rutland@arm.com> wrote:
>
> On Fri, Oct 06, 2023 at 03:15:51PM -0700, Douglas Anderson wrote:
> > In commit 44bd78dd2b88 ("irqchip/gic-v3: Disable pseudo NMIs on
> > Mediatek devices w/ firmware issues") we added a method for detecting
> > Mediatek devices with broken firmware and disabled pseudo-NMI. While
> > that worked, it didn't address the problem at a deep enough level.
> >
> > The fundamental issue with this broken firmware is that it's not
> > saving and restoring several important GICR registers. The current
> > list is believed to be:
> > * GICR_NUM_IPRIORITYR
> > * GICR_CTLR
> > * GICR_ISPENDR0
> > * GICR_ISACTIVER0
> > * GICR_NSACR
> >
> > Pseudo-NMI didn't work because it was the only thing (currently) in
> > the kernel that relied on the broken registers, so forcing pseudo-NMI
> > off was an effective fix. However, it could be observed that calling
> > system_uses_irq_prio_masking() on these systems still returned
> > "true". That caused confusion and led to the need for
> > commit a07a59415217 ("arm64: smp: avoid NMI IPIs with broken MediaTek
> > FW"). It's worried that the incorrect value returned by
> > system_uses_irq_prio_masking() on these systems will continue to
> > confuse future developers.
> >
> > Let's fix the issue a little more completely by disabling IRQ
> > priorities at a deeper level in the kernel. Once we do this we can
> > revert some of the other bits of code dealing with this quirk.
> >
> > Signed-off-by: Douglas Anderson <dianders@chromium.org>
> > ---
> >
> >  arch/arm64/kernel/cpufeature.c | 21 +++++++++++++++++++++
> >  1 file changed, 21 insertions(+)
> >
> > diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> > index 2806a2850e78..e35efab8efa9 100644
> > --- a/arch/arm64/kernel/cpufeature.c
> > +++ b/arch/arm64/kernel/cpufeature.c
> > @@ -2094,9 +2094,30 @@ static int __init early_enable_pseudo_nmi(char *p)
> >  }
> >  early_param("irqchip.gicv3_pseudo_nmi", early_enable_pseudo_nmi);
> >
> > +static bool are_gic_priorities_broken(void)
> > +{
> > +     bool is_broken = false;
> > +     struct device_node *np;
> > +
> > +     /*
> > +      * Detect broken Mediatek firmware that doesn't properly save and
> > +      * restore GIC priorities.
> > +      */
> > +     np = of_find_compatible_node(NULL, NULL, "arm,gic-v3");
> > +     if (np) {
> > +             is_broken = of_property_read_bool(np, "mediatek,broken-save-restore-fw");
> > +             of_node_put(np);
> > +     }
> > +
> > +     return is_broken;
> > +}
>
> I'm definitely in favour of detecting this in the cpucap, but I think it'd be
> better to parse the DT once on the boot CPU rather than on each CPU every time
> it's brought up.
>
> I think if we add something like:
>
> #ifdef CONFIG_ARM64_PSEUDO_NMI
> static void detect_system_supports_pseudo_nmi(void)
> {
>         struct device_node *np;
>
>         if (!enable_pseudo_nmi)
>                 return;
>
>         /*
>          * Detect broken Mediatek firmware that doesn't properly save and
>          * restore GIC priorities.
>          */
>         np = of_find_compatible_node(NULL, NULL, "arm,gic-v3");
>         if (np && of_property_read_bool(np, "mediatek,broken-save-restore-fw")) {
>                 pr_info("Pseudo-NMI disabled due to Mediatek Chromebook GICR save problem");
>                 enable_pseudo_nmi = false;
>         }
>         of_node_put(np);
> }
> #endif /* CONFIG_ARM64_PSEUDO_NMI */
> static inline void detect_system_supports_pseudo_nmi(void) { }
> #endif
>
> ... then we can call that from init_cpu_features() before we call
> setup_boot_cpu_capabilities(), and then the existing logic in
> can_use_gic_priorities() should just work as that returns the value of
> enable_pseudo_nmi.
>
> Note: of_node_put(NULL) does nothing, like kfree(NULL), so it's fine for that
> to be called in the !np case.
>
> Would you be happy to fold that in? I'm happy with a Suggested-by tag if so. :)

Yup, that looks good to me and I can fold it in (fixing a few nits
like missing "\n" and adding __init to the function). I'll wait to get
maintainers opinions on whether to fold patch #3 in here and then send
a v2.

-Doug

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Re: [PATCH 1/3] arm64: Disable GiC priorities on Mediatek devices w/ firmware issues

[Will Deacon]

On Mon, Oct 30, 2023 at 04:19:55PM -0700, Doug Anderson wrote:
> On Wed, Oct 18, 2023 at 4:01 AM Mark Rutland <mark.rutland@arm.com> wrote:
> > On Fri, Oct 06, 2023 at 03:15:51PM -0700, Douglas Anderson wrote:
> > > diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> > > index 2806a2850e78..e35efab8efa9 100644
> > > --- a/arch/arm64/kernel/cpufeature.c
> > > +++ b/arch/arm64/kernel/cpufeature.c
> > > @@ -2094,9 +2094,30 @@ static int __init early_enable_pseudo_nmi(char *p)
> > >  }
> > >  early_param("irqchip.gicv3_pseudo_nmi", early_enable_pseudo_nmi);
> > >
> > > +static bool are_gic_priorities_broken(void)
> > > +{
> > > +     bool is_broken = false;
> > > +     struct device_node *np;
> > > +
> > > +     /*
> > > +      * Detect broken Mediatek firmware that doesn't properly save and
> > > +      * restore GIC priorities.
> > > +      */
> > > +     np = of_find_compatible_node(NULL, NULL, "arm,gic-v3");
> > > +     if (np) {
> > > +             is_broken = of_property_read_bool(np, "mediatek,broken-save-restore-fw");
> > > +             of_node_put(np);
> > > +     }
> > > +
> > > +     return is_broken;
> > > +}
> >
> > I'm definitely in favour of detecting this in the cpucap, but I think it'd be
> > better to parse the DT once on the boot CPU rather than on each CPU every time
> > it's brought up.
> >
> > I think if we add something like:
> >
> > #ifdef CONFIG_ARM64_PSEUDO_NMI
> > static void detect_system_supports_pseudo_nmi(void)
> > {
> >         struct device_node *np;
> >
> >         if (!enable_pseudo_nmi)
> >                 return;
> >
> >         /*
> >          * Detect broken Mediatek firmware that doesn't properly save and
> >          * restore GIC priorities.
> >          */
> >         np = of_find_compatible_node(NULL, NULL, "arm,gic-v3");
> >         if (np && of_property_read_bool(np, "mediatek,broken-save-restore-fw")) {
> >                 pr_info("Pseudo-NMI disabled due to Mediatek Chromebook GICR save problem");
> >                 enable_pseudo_nmi = false;
> >         }
> >         of_node_put(np);
> > }
> > #endif /* CONFIG_ARM64_PSEUDO_NMI */
> > static inline void detect_system_supports_pseudo_nmi(void) { }
> > #endif
> >
> > ... then we can call that from init_cpu_features() before we call
> > setup_boot_cpu_capabilities(), and then the existing logic in
> > can_use_gic_priorities() should just work as that returns the value of
> > enable_pseudo_nmi.
> >
> > Note: of_node_put(NULL) does nothing, like kfree(NULL), so it's fine for that
> > to be called in the !np case.
> >
> > Would you be happy to fold that in? I'm happy with a Suggested-by tag if so. :)
> 
> Yup, that looks good to me and I can fold it in (fixing a few nits
> like missing "\n" and adding __init to the function). I'll wait to get
> maintainers opinions on whether to fold patch #3 in here and then send
> a v2.

No preference from me; I assume this stuff's all going in together anyway.

Will

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