Re: [PATCH v2] iommu/arm-smmu: disable PRR on SM8250

On Sun, 6 Jul 2025 at 18:20, Rob Clark [off-list ref] wrote:

On Sun, Jul 6, 2025 at 7:22 AM Akhil P Oommen [off-list ref] wrote:

quoted

On 7/5/2025 9:38 PM, Dmitry Baryshkov wrote:

quoted

On SM8250 / QRB5165-RB5 using PRR bits resets the device, most likely
because of the hyp limitations. Disable PRR support on that platform.

Fixes: 7f2ef1bfc758 ("iommu/arm-smmu: Add support for PRR bit setup")
Signed-off-by: Dmitry Baryshkov <redacted>

Reviewed-by: Akhil P Oommen <akhilpo@oss.qualcomm.com>

Unfortunately, there is no way to detect firmware support for PRR safely
from KMD.

I still am a bit curious about whether it is the ACLTR write that
trips the fw out (doubtful, since we write other bits in that reg
AFAICT) or the PRR_CFG_LADDR/UADDR write that does it.

Indeed, write to ACTLR seems to go through, writes (or reads) to
PRR_CFG_[LU]ADDR cause a reset.

In the latter
case we could potentially use a reserved-region for the PRR page,
instead of dynamically allocating it (if we knew what values are in
LADDR/UADDR.. I guess 0x0?) to avoid reduced vk functionality on these
devices.  AFAIU the vk extensions that depend on PRR are required for
vkd3d.

-- 
With best wishes
Dmitry