[Intel-gfx] [PATCHv5] drm/i915/dp: change aux_ctl reg read to polling read

[Jani Nikula]

On Wed, 14 Dec 2022, Arun R Murthy <arun.r.murthy at 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
>
> Signed-off-by: Arun R Murthy <arun.r.murthy at intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_dp_aux.c | 35 ++++++---------------
>  1 file changed, 9 insertions(+), 26 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..772da38b451f 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_aux.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_aux.c
> @@ -34,31 +34,6 @@ static void intel_dp_aux_unpack(u32 src, u8 *dst, int dst_bytes)
>  		dst[i] = src >> ((3 - i) * 8);
>  }
>  
> -static u32
> -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));
> -
> -	/* just trace the final value */
> -	trace_i915_reg_rw(false, ch_ctl, status, sizeof(status), true);
> -
> -	if (!done)
> -		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;
> -}
> -

Please keep the function.

intel_dp_aux_xfer() is long enough as it is. It really doesn't need the
added lines, quite the opposite.

The intel_dp_aux_wait_done() also gives a name to what's being done.

>  static u32 g4x_get_aux_clock_divider(struct intel_dp *intel_dp, int index)
>  {
>  	struct drm_i915_private *dev_priv = dp_to_i915(intel_dp);
> @@ -264,6 +239,7 @@ intel_dp_aux_xfer(struct intel_dp *intel_dp,
>  	}
>  
>  	while ((aux_clock_divider = intel_dp->get_aux_clock_divider(intel_dp, clock++))) {
> +		u32 timeout_ms = 10;
>  		u32 send_ctl = intel_dp->get_aux_send_ctl(intel_dp,
>  							  send_bytes,
>  							  aux_clock_divider);
> @@ -281,7 +257,14 @@ 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);
>  
> -			status = intel_dp_aux_wait_done(intel_dp);
> +			__intel_de_wait_for_register(i915, ch_ctl,
> +						     DP_AUX_CH_CTL_SEND_BUSY, 0,
> +						     500, timeout_ms, &status);
> +
> +			if ((status & DP_AUX_CH_CTL_SEND_BUSY) != 0)
> +				drm_err(&i915->drm,
> +					"%s: did not complete or timeout within %ums (status 0x%08x)\n",
> +					intel_dp->aux.name, timeout_ms, status);

Please use the return value of intel_de_wait_for_register() to determine
the timeout instead of duplicating the condition. (Feels like I said
this a few times already?)

BR,
Jani.

>  
>  			/* Clear done status and any errors */
>  			intel_de_write(i915, ch_ctl,

-- 
Jani Nikula, Intel Open Source Graphics Center