Re: [Intel-gfx] [PATCHv2] drm/i915/display/dp: On AUX xfer timeout restart freshly

[Imre Deak <imre.deak@intel.com>]

On Thu, Jun 08, 2023 at 03:02:18PM +0530, Arun R Murthy wrote:
> At the begining of the aux transfer a check for aux control busy bit is
> done. Then as per the spec on aux transfer timeout, need to retry
> freshly for 3 times with a delay which is taken care by the control
> register.
> On each of these 3 trials a check for busy has to be done so as to start
> freshly.
> 
> v2: updated the commit message
> 
> Signed-off-by: Arun R Murthy <arun.r.murthy@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_dp_aux.c | 50 +++++++++------------
>  1 file changed, 22 insertions(+), 28 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux.c b/drivers/gpu/drm/i915/display/intel_dp_aux.c
> index 197c6e81db14..25090542dd9f 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_aux.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_aux.c
> @@ -273,30 +273,6 @@ intel_dp_aux_xfer(struct intel_dp *intel_dp,
>  	 * it using the same AUX CH simultaneously
>  	 */
>  
> -	/* Try to wait for any previous AUX channel activity */
> -	for (try = 0; try < 3; try++) {
> -		status = intel_de_read_notrace(i915, ch_ctl);
> -		if ((status & DP_AUX_CH_CTL_SEND_BUSY) == 0)
> -			break;
> -		msleep(1);
> -	}
> -	/* just trace the final value */
> -	trace_i915_reg_rw(false, ch_ctl, status, sizeof(status), true);
> -
> -	if (try == 3) {
> -		const u32 status = intel_de_read(i915, ch_ctl);
> -
> -		if (status != intel_dp->aux_busy_last_status) {
> -			drm_WARN(&i915->drm, 1,
> -				 "%s: not started (status 0x%08x)\n",
> -				 intel_dp->aux.name, status);
> -			intel_dp->aux_busy_last_status = status;
> -		}
> -
> -		ret = -EBUSY;
> -		goto out;
> -	}
> -
>  	/* Only 5 data registers! */
>  	if (drm_WARN_ON(&i915->drm, send_bytes > 20 || recv_size > 20)) {
>  		ret = -E2BIG;
> @@ -304,14 +280,31 @@ intel_dp_aux_xfer(struct intel_dp *intel_dp,
>  	}
>  
>  	while ((aux_clock_divider = intel_dp->get_aux_clock_divider(intel_dp, clock++))) {
> -		u32 send_ctl = intel_dp->get_aux_send_ctl(intel_dp,
> +		/* Must try at least 3 times according to DP spec */
> +		for (try = 0; try < 5; try++) {
> +			u32 send_ctl = intel_dp->get_aux_send_ctl(intel_dp,
>  							  send_bytes,
>  							  aux_clock_divider);
>  
> -		send_ctl |= aux_send_ctl_flags;
> +			send_ctl |= aux_send_ctl_flags;

Why is send_ctl recomputed in each iteration?

> +
> +			/* Try to wait for any previous AUX channel activity */
> +			status = intel_dp_aux_wait_done(intel_dp);

How does it help to wait here for the same condition that was already
waited for at the end of the loop?

> +			/* just trace the final value */
> +			trace_i915_reg_rw(false, ch_ctl, status, sizeof(status), true);
> +
> +			if (status & DP_AUX_CH_CTL_SEND_BUSY) {
> +				drm_WARN(&i915->drm, 1,
> +					 "%s: not started, previous Tx still in process (status 0x%08x)\n",
> +					 intel_dp->aux.name, status);
> +				intel_dp->aux_busy_last_status = status;
> +				if (try > 3) {
> +					ret = -EBUSY;
> +					goto out;
> +				} else
> +					continue;
> +			}
>  
> -		/* Must try at least 3 times according to DP spec */
> -		for (try = 0; try < 5; try++) {
>  			/* Load the send data into the aux channel data registers */
>  			for (i = 0; i < send_bytes; i += 4)
>  				intel_de_write(i915, ch_data[i >> 2],
> @@ -321,6 +314,7 @@ intel_dp_aux_xfer(struct intel_dp *intel_dp,
>  			/* Send the command and wait for it to complete */
>  			intel_de_write(i915, ch_ctl, send_ctl);
>  
> +			/* TODO: if typeC then 4.2ms else 800us. For DG2 add 1.5ms for both cases */
>  			status = intel_dp_aux_wait_done(intel_dp);
>  
>  			/* Clear done status and any errors */
> -- 
> 2.25.1
>