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

[Murthy, Arun R]

Any comments?

Thanks and Regards,
Arun R Murthy
--------------------

> -----Original Message-----
> From: Murthy, Arun R <arun.r.murthy at intel.com>
> Sent: Thursday, December 15, 2022 4:44 PM
> To: intel-gfx at lists.freedesktop.org; ville.syrjala at linux.intel.com; Nikula, Jani
> <jani.nikula at intel.com>; Deak, Imre <imre.deak at intel.com>
> Cc: Murthy, Arun R <arun.r.murthy at intel.com>
> Subject: [PATCHv6] drm/i915/dp: change aux_ctl reg read to polling read
> 
> 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 at intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_dp_aux.c | 14 +++++---------
>  1 file changed, 5 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..973dadecf712 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_aux.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_aux.c
> @@ -41,20 +41,16 @@ 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));
> +	int 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)
>  		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;
>  }
> --
> 2.25.1