Hi Nitin,
On Mon, Feb 24, 2025 at 12:01:04PM +0530, Nitin Gote wrote:
> Sometimes engine reset fails because the engine resumes from an
> incorrect RING_HEAD. Engine head failed to set to zero even after
> writing into it. This is a timing issue and we experimented
> different values and found out that 20ms delay works best based
> on testing.
>
> So, add a 20ms delay to let engine resumes from correct RING_HEAD.
>
> Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/13650
> Signed-off-by: Nitin Gote <nitin.r.g...@intel.com>
> ---
> drivers/gpu/drm/i915/gt/intel_ring_submission.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/gt/intel_ring_submission.c
> b/drivers/gpu/drm/i915/gt/intel_ring_submission.c
> index 6e9977b2d180..5576f000e965 100644
> --- a/drivers/gpu/drm/i915/gt/intel_ring_submission.c
> +++ b/drivers/gpu/drm/i915/gt/intel_ring_submission.c
> @@ -365,6 +365,13 @@ static void reset_prepare(struct intel_engine_cs *engine)
> ENGINE_READ_FW(engine, RING_HEAD),
> ENGINE_READ_FW(engine, RING_TAIL),
> ENGINE_READ_FW(engine, RING_START));
> + /*
> + * Sometimes engine head failed to set to zero even after
> writing into it.
> + * Use 20ms delay to let engine resumes from correct RING_HEAD.
> + * Experimented different values and determined that 20ms works
> best
> + * based on testing.
> + */
> + mdelay(20);
Is there any extremely strong reason for using mdelay here,
rather than any other delay function?
Andi
> if (!stop_ring(engine)) {
> drm_err(&engine->i915->drm,
> "failed to set %s head to zero "
> --
> 2.25.1
