* [PATCH] iommu/arm-smmu-v3: Skip prefetch cmd for MMU-600, MMU-700
@ 2024-05-13 21:54 Daniel Mentz
2024-05-15 15:29 ` Robin Murphy
0 siblings, 1 reply; 3+ messages in thread
From: Daniel Mentz @ 2024-05-13 21:54 UTC (permalink / raw)
To: iommu; +Cc: Nicolin Chen, Robin Murphy, Daniel Mentz
Arm CoreLink MMU-600 and MMU-700 both silently ignore the
CMD_PREFETCH_CONFIG command. Let's not waste cycles adding this command to
the command queue if it is ignored anyway.
Signed-off-by: Daniel Mentz <danielmentz@google.com>
---
drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
index aa62f0ecd053..98f1c4b44ef3 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
@@ -3684,6 +3684,8 @@ static void arm_smmu_device_iidr_probe(struct arm_smmu_device *smmu)
case IIDR_IMPLEMENTER_ARM:
switch (productid) {
case IIDR_PRODUCTID_ARM_MMU_600:
+ /* MMU-600 silently ignores CMD_PREFETCH_CONFIG */
+ smmu->options |= ARM_SMMU_OPT_SKIP_PREFETCH;
/* Arm erratum 1076982 */
if (variant == 0 && revision <= 2)
smmu->features &= ~ARM_SMMU_FEAT_SEV;
@@ -3692,6 +3694,8 @@ static void arm_smmu_device_iidr_probe(struct arm_smmu_device *smmu)
smmu->features &= ~ARM_SMMU_FEAT_NESTING;
break;
case IIDR_PRODUCTID_ARM_MMU_700:
+ /* MMU-700 silently ignores CMD_PREFETCH_CONFIG */
+ smmu->options |= ARM_SMMU_OPT_SKIP_PREFETCH;
/* Arm erratum 2812531 */
smmu->features &= ~ARM_SMMU_FEAT_BTM;
smmu->options |= ARM_SMMU_OPT_CMDQ_FORCE_SYNC;
--
2.45.0.118.g7fe29c98d7-goog
^ permalink raw reply related [flat|nested] 3+ messages in thread* Re: [PATCH] iommu/arm-smmu-v3: Skip prefetch cmd for MMU-600, MMU-700
2024-05-13 21:54 [PATCH] iommu/arm-smmu-v3: Skip prefetch cmd for MMU-600, MMU-700 Daniel Mentz
@ 2024-05-15 15:29 ` Robin Murphy
2024-05-21 17:49 ` Daniel Mentz
0 siblings, 1 reply; 3+ messages in thread
From: Robin Murphy @ 2024-05-15 15:29 UTC (permalink / raw)
To: Daniel Mentz, iommu
Cc: Nicolin Chen, linux-arm-kernel, Will Deacon, Mostafa Saleh
Hi Daniel,
On 2024-05-13 10:54 pm, Daniel Mentz wrote:
> Arm CoreLink MMU-600 and MMU-700 both silently ignore the
> CMD_PREFETCH_CONFIG command. Let's not waste cycles adding this command to
> the command queue if it is ignored anyway.
It is true that our implementations don't do anything with prefetch
commands so far, however this is a valid architectural behaviour, and
the intent of the quirk is really for buggy implementations where the
commands erroneously fault.
TBH if saving cycles in arm_smmu_attach_dev() matters to you, then
you're probably not going to like what's now queued in next that makes
it absurdly overcomplicated with loads of indirect function calls...
Thanks,
Robin.
> Signed-off-by: Daniel Mentz <danielmentz@google.com>
> ---
> drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> index aa62f0ecd053..98f1c4b44ef3 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> @@ -3684,6 +3684,8 @@ static void arm_smmu_device_iidr_probe(struct arm_smmu_device *smmu)
> case IIDR_IMPLEMENTER_ARM:
> switch (productid) {
> case IIDR_PRODUCTID_ARM_MMU_600:
> + /* MMU-600 silently ignores CMD_PREFETCH_CONFIG */
> + smmu->options |= ARM_SMMU_OPT_SKIP_PREFETCH;
> /* Arm erratum 1076982 */
> if (variant == 0 && revision <= 2)
> smmu->features &= ~ARM_SMMU_FEAT_SEV;
> @@ -3692,6 +3694,8 @@ static void arm_smmu_device_iidr_probe(struct arm_smmu_device *smmu)
> smmu->features &= ~ARM_SMMU_FEAT_NESTING;
> break;
> case IIDR_PRODUCTID_ARM_MMU_700:
> + /* MMU-700 silently ignores CMD_PREFETCH_CONFIG */
> + smmu->options |= ARM_SMMU_OPT_SKIP_PREFETCH;
> /* Arm erratum 2812531 */
> smmu->features &= ~ARM_SMMU_FEAT_BTM;
> smmu->options |= ARM_SMMU_OPT_CMDQ_FORCE_SYNC;
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: [PATCH] iommu/arm-smmu-v3: Skip prefetch cmd for MMU-600, MMU-700
2024-05-15 15:29 ` Robin Murphy
@ 2024-05-21 17:49 ` Daniel Mentz
0 siblings, 0 replies; 3+ messages in thread
From: Daniel Mentz @ 2024-05-21 17:49 UTC (permalink / raw)
To: Robin Murphy
Cc: iommu, Nicolin Chen, linux-arm-kernel, Will Deacon, Mostafa Saleh
On Wed, May 15, 2024 at 8:29 AM Robin Murphy <robin.murphy@arm.com> wrote:
>
> Hi Daniel,
>
> On 2024-05-13 10:54 pm, Daniel Mentz wrote:
> > Arm CoreLink MMU-600 and MMU-700 both silently ignore the
> > CMD_PREFETCH_CONFIG command. Let's not waste cycles adding this command to
> > the command queue if it is ignored anyway.
>
> It is true that our implementations don't do anything with prefetch
> commands so far, however this is a valid architectural behaviour, and
> the intent of the quirk is really for buggy implementations where the
> commands erroneously fault.
>
> TBH if saving cycles in arm_smmu_attach_dev() matters to you, then
> you're probably not going to like what's now queued in next that makes
> it absurdly overcomplicated with loads of indirect function calls...
Hi Robin,
That's fair. Given the low frequency with which arm_smmu_attach_dev()
is called, it might not be worth the added complexity. Thanks for the
feedback, though.
>
> Thanks,
> Robin.
>
> > Signed-off-by: Daniel Mentz <danielmentz@google.com>
> > ---
> > drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 4 ++++
> > 1 file changed, 4 insertions(+)
> >
> > diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> > index aa62f0ecd053..98f1c4b44ef3 100644
> > --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> > +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> > @@ -3684,6 +3684,8 @@ static void arm_smmu_device_iidr_probe(struct arm_smmu_device *smmu)
> > case IIDR_IMPLEMENTER_ARM:
> > switch (productid) {
> > case IIDR_PRODUCTID_ARM_MMU_600:
> > + /* MMU-600 silently ignores CMD_PREFETCH_CONFIG */
> > + smmu->options |= ARM_SMMU_OPT_SKIP_PREFETCH;
> > /* Arm erratum 1076982 */
> > if (variant == 0 && revision <= 2)
> > smmu->features &= ~ARM_SMMU_FEAT_SEV;
> > @@ -3692,6 +3694,8 @@ static void arm_smmu_device_iidr_probe(struct arm_smmu_device *smmu)
> > smmu->features &= ~ARM_SMMU_FEAT_NESTING;
> > break;
> > case IIDR_PRODUCTID_ARM_MMU_700:
> > + /* MMU-700 silently ignores CMD_PREFETCH_CONFIG */
> > + smmu->options |= ARM_SMMU_OPT_SKIP_PREFETCH;
> > /* Arm erratum 2812531 */
> > smmu->features &= ~ARM_SMMU_FEAT_BTM;
> > smmu->options |= ARM_SMMU_OPT_CMDQ_FORCE_SYNC;
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2024-05-21 17:49 UTC | newest]
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2024-05-13 21:54 [PATCH] iommu/arm-smmu-v3: Skip prefetch cmd for MMU-600, MMU-700 Daniel Mentz
2024-05-15 15:29 ` Robin Murphy
2024-05-21 17:49 ` Daniel Mentz
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