Re: [PATCH 1/3] arm: smmu: allow SMMU to have more IRQs than context banks

[Julien Grall <julien@xxxxxxx>]

Hi,

On 02/04/2024 08:28, Michal Orzel wrote:
> Hello,
>
> On 29/03/2024 01:08, Volodymyr Babchuk wrote:
> > I encountered platform, namely Qualcomm SA8155P where SMMU-compatible
> NIT: a commit msg should be written in imperative mood
>
> > IO-MMU advertises more context IQRs than there are context banks. This
> > should not be an issue, we need to relax the check in the SMMU driver
> > to allow such configuration.
> >
> > Signed-off-by: Volodymyr Babchuk <volodymyr_babchuk@xxxxxxxx>
> > ---
> >   xen/drivers/passthrough/arm/smmu.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/xen/drivers/passthrough/arm/smmu.c 
> > b/xen/drivers/passthrough/arm/smmu.c
> > index 32e2ff279b..2dd3688f3b 100644
> > --- a/xen/drivers/passthrough/arm/smmu.c
> > +++ b/xen/drivers/passthrough/arm/smmu.c
> > @@ -2550,7 +2550,7 @@ static int arm_smmu_device_dt_probe(struct 
> > platform_device *pdev)
> >          parse_driver_options(smmu);
> >
> >          if (smmu->version > ARM_SMMU_V1 &&
> > -           smmu->num_context_banks != smmu->num_context_irqs) {
> > +           smmu->num_context_banks > smmu->num_context_irqs) {
> This was done in Linux by commit:
> d1e20222d537 ("iommu/arm-smmu: Error out only if not enough context interrupts")
>
> However, they also ignore superfluous interrupts. Shouldn't we do the same?
+1. It would be better to avoid allocating stating for IRQs that are 
never used.
Cheers,

--
Julien Grall