Re: [Intel-gfx] [PATCHv6] drm/i915/dp: change aux_ctl reg read to polling read

[Jani Nikula <jani.nikula@intel.com>]

On Thu, 15 Dec 2022, Arun R Murthy <arun.r.murthy@intel.com> wrote:
> The busy timeout logic checks for the AUX BUSY, then waits for the
> timeout period and then after timeout reads the register for BUSY or
> Success.
> Instead replace interrupt with polling so as to read the AUX CTL
> register often before the timeout period. Looks like there might be some
> issue with interrupt-on-read. Hence changing the logic to polling read.
>
> v2: replace interrupt with polling read
> v3: use usleep_rang instead of msleep, updated commit msg
> v4: use intel_wait_for_regiter internal function
> v5: use __intel_de_wait_for_register with 500us slow and 10ms fast timeout
> v6: check return value of __intel_de_wait_for_register
>
> Signed-off-by: Arun R Murthy <arun.r.murthy@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_dp_aux.c | 15 +++++----------
>  1 file changed, 5 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux.c b/drivers/gpu/drm/i915/display/intel_dp_aux.c
> index 91c93c93e5fc..dec88f41380e 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_aux.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_aux.c
> @@ -40,21 +40,16 @@ intel_dp_aux_wait_done(struct intel_dp *intel_dp)
>  	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
>  	i915_reg_t ch_ctl = intel_dp->aux_ch_ctl_reg(intel_dp);
>  	const unsigned int timeout_ms = 10;
> -	u32 status;
> -	bool done;
> -
> -#define C (((status = intel_de_read_notrace(i915, ch_ctl)) & DP_AUX_CH_CTL_SEND_BUSY) == 0)
> -	done = wait_event_timeout(i915->display.gmbus.wait_queue, C,
> -				  msecs_to_jiffies_timeout(timeout_ms));
> +	u32 status, ret;
>  
> -	/* just trace the final value */
> -	trace_i915_reg_rw(false, ch_ctl, status, sizeof(status), true);
> +	ret = __intel_de_wait_for_register(i915, ch_ctl,
> +				     DP_AUX_CH_CTL_SEND_BUSY, 0,
> +				     500, timeout_ms, &status);
>  
> -	if (!done)
> +	if (ret == -ETIMEDOUT)

What's wrong with this comparison? Although it probably does work by
coincidence.

BR,
Jani.


>  		drm_err(&i915->drm,
>  			"%s: did not complete or timeout within %ums (status 0x%08x)\n",
>  			intel_dp->aux.name, timeout_ms, status);
> -#undef C
>  
>  	return status;
>  }

-- 
Jani Nikula, Intel Open Source Graphics Center