[Intel-gfx] [PATCH 1/5] drm/i915: Stop second guessing the caller for intel_uncore_wait_for_register()

[Tvrtko Ursulin]

On 11/04/2017 11:13, Chris Wilson wrote:
> Allow the caller to use the fast_timeout_us to specify how long to wait
> within the atomic section, rather than transparently switching to a
> sleeping loop for larger values. This is required as some callsites may
> need a long wait and are in an atomic section.
>
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Michal Wajdeczko <michal.wajdeczko at intel.com>
> Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> ---
>  drivers/gpu/drm/i915/intel_uncore.c | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
> index eb38392a2435..53c8457869f6 100644
> --- a/drivers/gpu/drm/i915/intel_uncore.c
> +++ b/drivers/gpu/drm/i915/intel_uncore.c
> @@ -1601,7 +1601,7 @@ static int gen6_reset_engines(struct drm_i915_private *dev_priv,
>   *
>   * Otherwise, the wait will timeout after @slow_timeout_ms milliseconds.
>   * For atomic context @slow_timeout_ms must be zero and @fast_timeout_us
> - * must be not larger than 10 microseconds.
> + * must be not larger than 20,0000 microseconds.
>   *
>   * Note that this routine assumes the caller holds forcewake asserted, it is
>   * not suitable for very long waits. See intel_wait_for_register() if you
> @@ -1623,16 +1623,17 @@ int __intel_wait_for_register_fw(struct drm_i915_private *dev_priv,
>  	int ret;
>
>  	/* Catch any overuse of this function */
> -	might_sleep_if(fast_timeout_us > 10 || slow_timeout_ms);
> +	might_sleep_if(slow_timeout_ms);
>
> -	if (fast_timeout_us > 10)
> -		ret = _wait_for(done, fast_timeout_us, 10);
> -	else
> +	ret = -ETIMEDOUT;
> +	if (fast_timeout_us && fast_timeout_us < 20000)

I agree with Michal here. Kerneldoc even says "must not be larger than 
20ms" so it would be better and completely fine in my opinion to:

	if (GEM_WARN_ON(fast_timeout_us > 20000))
		return -EINVAL;

Hm but it would break the bisectability of the series and break the 
sandybridge pcode.

So patch 4/5 looks broken since it changes the timeout from 500ms to 
500us. I don't see how to fix that without splitting the _fw and atomic 
concepts.

Regards,

Tvrtko

>  		ret = _wait_for_atomic(done, fast_timeout_us, 0);
>  	if (ret)
>  		ret = wait_for(done, slow_timeout_ms);
> +
>  	if (out_value)
>  		*out_value = reg_value;
> +
>  	return ret;
>  #undef done
>  }
>