Re: [PATCH v8 04/12] iommu/tegra241-cmdqv: Restore PROD and CONS after resume

[Pranjal Shrivastava <praan@google.com>]

On Mon, Jun 15, 2026 at 05:01:34PM +0000, Mostafa Saleh wrote:
> On Mon, Jun 01, 2026 at 09:59:01PM +0000, Pranjal Shrivastava wrote:
> > From: Ashish Mhetre <amhetre@nvidia.com>
> > 
> > PROD and CONS indices for vcmdqs are getting set to 0 after resume.
> > Because of this the vcmdq is not consuming commands after resume.
> > Fix this by restoring PROD and CONS indices after resume from
> > saved pointers.
> 
> What commands are exisiting at resume? Won't
> tegra241_cmdqv_drain_vintf0_lvcmdqs() drain the queues and make the
> PROD and CONS equal each other anyway?

The SW prod / cons are indeed equal because of the queue drain before
suspend. However, the HW registers in vCMDQ reset to 0 on a power-cycle

Now, if we resume with the software prod/cons at 100/100, since the HW
prod/cons is at 0/0, when the driver then issues a new command and only
updates the PROD register to 101, the HW will see (CONS=0, PROD=101).

The arm-smmu-v3 driver restores these indices correctly in device_reset
but the Tegra VMDQV driver doesn't. Thus, this patch was added to
restore both indices ensuring the HW doesn't de-sync.

This was added after Ashish tested an older version of the series [1]
with Tegra,

Thanks,
Praan

[1] https://lore.kernel.org/all/6afc3e46-489e-4741-96d5-8a2f72a8b431@nvidia.com/