Re: [PATCH] drm/i915/gen9: Increase PCODE request timeout to 100ms

Chris Wilson
2017-02-20T16:05:33Z

On Mon, Feb 20, 2017 at 05:29:44PM +0200, Imre Deak wrote:
> After
> commit 2c7d0602c815277f7cb7c932b091288710d8aba7
> Author: Imre Deak <imre.deak@intel.com>
> Date: Mon Dec 5 18:27:37 2016 +0200
>
> drm/i915/gen9: Fix PCODE polling during CDCLK change notification
>
> there is still one report of the CDCLK-change request timing out on a
> KBL machine, see the Reference link. On that machine the maximum time
> the request took to succeed was 34ms, so increase the timeout to 100ms.
>
> Reference: https://bugs.freedesktop.org/show_bug.cgi?id=99345
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Imre Deak <imre.deak@intel.com>
> ---
> drivers/gpu/drm/i915/intel_drv.h | 2 +-
> drivers/gpu/drm/i915/intel_pm.c | 11 ++++++-----
> 2 files changed, 7 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
> index 821c57c..7970ba8 100644
> --- a/drivers/gpu/drm/i915/intel_drv.h
> +++ b/drivers/gpu/drm/i915/intel_drv.h
> @@ -87,7 +87,7 @@
> int cpu, ret, timeout = (US) * 1000; \
> u64 base; \
> _WAIT_FOR_ATOMIC_CHECK(ATOMIC); \
> - BUILD_BUG_ON((US) > 50000); \
> + BUILD_BUG_ON((US) > 100000); \
> if (!(ATOMIC)) { \
> preempt_disable(); \
> cpu = smp_processor_id(); \
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> index fe243c6..90134b0 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -7910,10 +7910,10 @@ static bool skl_pcode_try_request(struct drm_i915_private *dev_priv, u32 mbox,
> * @timeout_base_ms: timeout for polling with preemption enabled
> *
> * Keep resending the @request to @mbox until PCODE acknowledges it, PCODE
> - * reports an error or an overall timeout of @timeout_base_ms+10 ms expires.
> + * reports an error or an overall timeout of @timeout_base_ms+100 ms expires.
> * The request is acknowledged once the PCODE reply dword equals @reply after
> * applying @reply_mask. Polling is first attempted with preemption enabled
> - * for @timeout_base_ms and if this times out for another 10 ms with
> + * for @timeout_base_ms and if this times out for another 100 ms with
> * preemption disabled.
> *
> * Returns 0 on success, %-ETIMEDOUT in case of a timeout, <0 in case of some
> @@ -7949,14 +7949,15 @@ int skl_pcode_request(struct drm_i915_private *dev_priv, u32 mbox, u32 request,
> * worst case) _and_ PCODE was busy for some reason even after a
> * (queued) request and @timeout_base_ms delay. As a workaround retry
> * the poll with preemption disabled to maximize the number of
> - * requests. Increase the timeout from @timeout_base_ms to 10ms to
> + * requests. Increase the timeout from @timeout_base_ms to 100ms to
> * account for interrupts that could reduce the number of these
> - * requests.
> + * requests, and for any quirks of the PCODE firmware that delays
> + * the request completion.
> */
> DRM_DEBUG_KMS("PCODE timeout, retrying with preemption disabled\n");
> WARN_ON_ONCE(timeout_base_ms > 3);
> preempt_disable();
> - ret = wait_for_atomic(COND, 10);
> + ret = wait_for_atomic(COND, 100);
> preempt_enable();

Ugh. Straw + camel. How about something like:

__try_request_atomic:
cond_resched();

preempt_disable()
ret = COND ? wait_for_atomic(COND, 10) : 0;
preempt_enable();
return ret;

try_request:
ret = wait_for(__try_request_atomic() == 0, 100);

So that our preempt-off period doesn't grow completely unchecked, or do
we need that 34ms loop?
-Chris

--
Chris Wilson, Intel Open Source Technology Centre