Re: [PATCH v12 13/16] iommu: Improve iopf_queue_remove_device()

[Baolu Lu]

On 2024/2/7 10:50, Tian, Kevin wrote:
> > From: Lu Baolu<baolu.lu@xxxxxxxxxxxxxxx>
> > Sent: Wednesday, February 7, 2024 9:33 AM
> >
> > Convert iopf_queue_remove_device() to return void instead of an error code,
> > as the return value is never used. This removal helper is designed to be
> > never-failed, so there's no need for error handling.
> >
> > Ack all outstanding page requests from the device with the response code of
> > IOMMU_PAGE_RESP_INVALID, indicating device should not attempt any retry.
> >
> > Add comments to this helper explaining the steps involved in removing a
> > device from the iopf queue and disabling its PRI. The individual drivers
> > are expected to be adjusted accordingly. Here we just define the expected
> > behaviors of the individual iommu driver from the core's perspective.
> >
> > Suggested-by: Jason Gunthorpe<jgg@xxxxxxxxxx>
> > Signed-off-by: Lu Baolu<baolu.lu@xxxxxxxxxxxxxxx>
> > Reviewed-by: Jason Gunthorpe<jgg@xxxxxxxxxx>
> > Tested-by: Yan Zhao<yan.y.zhao@xxxxxxxxx>
> Reviewed-by: Kevin Tian<kevin.tian@xxxxxxxxx>, with one nit:
>
> > + * Removing a device from an iopf_queue. It's recommended to follow
> > these
> > + * steps when removing a device:
> >    *
> > - * Return: 0 on success and <0 on error.
> > + * - Disable new PRI reception: Turn off PRI generation in the IOMMU
> > hardware
> > + *   and flush any hardware page request queues. This should be done
> > before
> > + *   calling into this helper.
> > + * - Acknowledge all outstanding PRQs to the device: Respond to all
> > outstanding
> > + *   page requests with IOMMU_PAGE_RESP_INVALID, indicating the device
> > should
> > + *   not retry. This helper function handles this.
> this implies calling iopf_queue_remove_device() here.
>
> > + * - Disable PRI on the device: After calling this helper, the caller could
> > + *   then disable PRI on the device.
> > + * - Call iopf_queue_remove_device(): Calling iopf_queue_remove_device()
> > + *   essentially disassociates the device. The fault_param might still exist,
> > + *   but iommu_page_response() will do nothing. The device fault parameter
> > + *   reference count has been properly passed from
> > iommu_report_device_fault()
> > + *   to the fault handling work, and will eventually be released after
> > + *   iommu_page_response().
> >    */
> but here it suggests calling iopf_queue_remove_device() again. If the comment
> is just about to detail the behavior with that invocation shouldn't it be merged
> with the previous one instead of pretending to be the final step for driver
> to call?

Above just explains the behavior of calling iopf_queue_remove_device().

Best regards,
baolu