Re: [PATCH v7 4/5] iommu/arm-smmu-v3: Standardize ATS enablement failure reporting

[Pranjal Shrivastava <praan@google.com>]

On Wed, Jun 03, 2026 at 07:34:14AM +0000, Tian, Kevin wrote:
> > From: Pranjal Shrivastava <praan@google.com>
> > Sent: Monday, June 1, 2026 10:37 PM
> > 
> > Update arm_smmu_enable_ats() to wrap the pci_enable_ats() call in
> > WARN_ON(). Since probe-time checks now preclude configuration errors
> > any failure during hardware enablement is considered a kernel bug.
> > 
> > Signed-off-by: Pranjal Shrivastava <praan@google.com>
> > ---
> >  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 7 ++++++-
> >  1 file changed, 6 insertions(+), 1 deletion(-)
> > 
> > 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 54c7f1ae3a84..dfb2b0d2d2a5 100644
> > --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> > +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> > @@ -2956,7 +2956,12 @@ static void arm_smmu_enable_ats(struct
> > arm_smmu_master *master)
> >  	 * ATC invalidation of PASID 0 causes the entire ATC to be flushed.
> >  	 */
> >  	arm_smmu_atc_inv_master(master, IOMMU_NO_PASID);
> > -	if (pci_enable_ats(pdev, stu))
> > +
> > +	 /*
> > +	  * Since pci_prepare_ats() has already verified the HW capability
> > +	  * and programmed the STE, pci_enable_ats() should not fail here.
> > +	  */
> > +	if (WARN_ON(pci_enable_ats(pdev, stu)))
> >  		dev_err(master->dev, "Failed to enable ATS (STU %zu)\n",
> > stu);
> >  }
> > 
> 
> looks smmu driver doesn't check return value of pci_prepare_ats() too.

It does check the reval of pci_prepare_ats() now with the a recent 
patch [1] (merged in Joerg's tree) that adds a new 
"arm_smmu_master_prepare_ats" helper function.

Thanks,
Praan

[1] https://git.kernel.org/pub/scm/linux/kernel/git/iommu/linux.git/commit/?h=core&id=5ff98a0da6b48d8722eac0080e4185c417925d05