Re: [Intel-gfx] [PATCHv4] drm/i915/dp: change aux_ctl reg read to polling read

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

On Wed, 14 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
>
> Signed-off-by: Arun R Murthy <arun.r.murthy@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_dp_aux.c | 18 +++++++++---------
>  1 file changed, 9 insertions(+), 9 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..fe5ed432a66a 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_aux.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_aux.c
> @@ -41,20 +41,20 @@ intel_dp_aux_wait_done(struct intel_dp *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));
> +	__intel_wait_for_register(&i915->uncore, ch_ctl,
> +				  DP_AUX_CH_CTL_SEND_BUSY,
> +				  DP_AUX_CH_CTL_SEND_BUSY,
> +				  500, timeout_ms, &status);

This waits for DP_AUX_CH_CTL_SEND_BUSY to be set, not cleared.

Please use intel_de_wait_for_register().

>  
> -	/* just trace the final value */
> -	trace_i915_reg_rw(false, ch_ctl, status, sizeof(status), true);
> -
> -	if (!done)
> +	status = intel_uncore_read_notrace(&i915->uncore, ch_ctl);
> +	if ((status & DP_AUX_CH_CTL_SEND_BUSY) != 0)

Please check intel_de_wait_for_register()'s return value here instead of
reading the register once more.

You might read the register the register again just to log the value, if
intel_de_wait_for_register() returned != 0. But no need to trace log
that again.

>  		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
> +
> +	/* just trace the final value */
> +	trace_i915_reg_rw(false, ch_ctl, status, sizeof(status), true);

intel_de_wait_for_register() already does the tracing of the final
value.

>  
>  	return status;
>  }

-- 
Jani Nikula, Intel Open Source Graphics Center