[PATCH] iommu/arm-smmu: Clarify MMU-500 CPRE workaround

[Will Deacon]

On Fri, Sep 13, 2024 at 04:13:29PM +0100, Robin Murphy wrote:
> On 2024-09-13 1:55 pm, Robin Murphy wrote:
> > CPRE workarounds are implicated in at least 5 MMU-500 errata, some of
> > which remain unfixed. The comment and warning message have proven to be
> > unhelpfully misleading about this scope, so reword them to get the point
> > across with less risk of going out of date or confusing users.
> > 
> > Signed-off-by: Robin Murphy <robin.murphy at arm.com>
> > ---
> >   drivers/iommu/arm/arm-smmu/arm-smmu-impl.c | 4 ++--
> >   1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu-impl.c b/drivers/iommu/arm/arm-smmu/arm-smmu-impl.c
> > index 9dc772f2cbb2..2edb1c1658ad 100644
> > --- a/drivers/iommu/arm/arm-smmu/arm-smmu-impl.c
> > +++ b/drivers/iommu/arm/arm-smmu/arm-smmu-impl.c
> > @@ -130,7 +130,7 @@ int arm_mmu500_reset(struct arm_smmu_device *smmu)
> >   	/*
> >   	 * Disable MMU-500's not-particularly-beneficial next-page
> > -	 * prefetcher for the sake of errata #841119 and #826419.
> > +	 * prefetcher for the sake of at least 5 known errata.
> >   	 */
> >   	for (i = 0; i < smmu->num_context_banks; ++i) {
> >   		reg = arm_smmu_cb_read(smmu, i, ARM_SMMU_CB_ACTLR);
> > @@ -138,7 +138,7 @@ int arm_mmu500_reset(struct arm_smmu_device *smmu)
> >   		arm_smmu_cb_write(smmu, i, ARM_SMMU_CB_ACTLR, reg);
> >   		reg = arm_smmu_cb_read(smmu, i, ARM_SMMU_CB_ACTLR);
> >   		if (reg & ARM_MMU500_ACTLR_CPRE)
> > -			dev_warn_once(smmu->dev, "Failed to disable prefetcher [errata #841119 and #826419], check ACR.CACHE_LOCK\n");
> > +			dev_warn_once(smmu->dev, "Failed to disable prefetcher for errata workarounds, check ACR.CACHE_LOCK\n");
> 
> Come to think of it, this should probably also refer to SACR rather than
> ACR, given that we already *have* attempted to program the Non-Secure
> side...

I'm happy to pick up a v2 with that change.

Cheers,

Will