Re: [PATCH 2/5] drm: Use new mode_valid() helpers in connector probe helper

[Daniel Vetter]

On Thu, May 04, 2017 at 03:11:39PM +0100, Jose Abreu wrote:
> This changes the connector probe helper function to use the new
> encoder->mode_valid() and crtc->mode_valid() helper callbacks to
> validate the modes.
> 
> The new callbacks are optional so the behaviour remains the same
> if they are not implemented. If they are, then the code loops
> through all the connector's encodersXcrtcs and calls the
> callback.
> 
> If at least a valid encoderXcrtc combination is found which
> accepts the mode then the function returns MODE_OK.
> 
> Signed-off-by: Jose Abreu <joabreu@xxxxxxxxxxxx>
> Cc: Carlos Palminha <palminha@xxxxxxxxxxxx>
> Cc: Alexey Brodkin <abrodkin@xxxxxxxxxxxx>
> Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
> Cc: Dave Airlie <airlied@xxxxxxxx>
> Cc: Andrzej Hajda <a.hajda@xxxxxxxxxxx>
> Cc: Archit Taneja <architt@xxxxxxxxxxxxxx>

A few comments below.
-Daniel

> ---
>  drivers/gpu/drm/drm_probe_helper.c | 71 +++++++++++++++++++++++++++++++++++---
>  1 file changed, 67 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_probe_helper.c b/drivers/gpu/drm/drm_probe_helper.c
> index 1b0c14a..bf19f82 100644
> --- a/drivers/gpu/drm/drm_probe_helper.c
> +++ b/drivers/gpu/drm/drm_probe_helper.c
> @@ -80,6 +80,67 @@
>  	return MODE_OK;
>  }
>  
> +static enum drm_mode_status
> +drm_mode_validate_connector(struct drm_connector *connector,
> +			    struct drm_display_mode *mode)
> +{
> +	const struct drm_connector_helper_funcs *connector_funcs =
> +		connector->helper_private;
> +	struct drm_device *dev = connector->dev;
> +	uint32_t *ids = connector->encoder_ids;
> +	enum drm_mode_status ret = MODE_OK;
> +	unsigned int i;
> +
> +	/* Step 1: Validate against connector */
> +	if (connector_funcs && connector_funcs->mode_valid)
> +		ret = connector_funcs->mode_valid(connector, mode);
> +
> +	if (ret != MODE_OK)
> +		return ret;
> +
> +	/* Step 2: Validate against encoders and crtcs */
> +	for (i = 0; i < DRM_CONNECTOR_MAX_ENCODER; i++) {
> +		struct drm_encoder *encoder = drm_encoder_find(dev, ids[i]);
> +		const struct drm_encoder_helper_funcs *encoder_funcs;
> +		struct drm_crtc *crtc;
> +
> +		if (!encoder)
> +			continue;
> +
> +		encoder_funcs = encoder->helper_private;
> +		if (encoder_funcs && encoder_funcs->mode_valid)
> +			ret = encoder_funcs->mode_valid(encoder, mode);
> +		else
> +			ret = MODE_OK; /* encoder accepts everything */
> +
> +		/* No point in continuing for crtc check as this encoder will
> +		 * not accept the mode anyway. If all encoders reject the mode
> +		 * then, at exit, ret will not be MODE_OK. */
> +		if (ret != MODE_OK)
> +			continue;

I think we should validate encoders against connector->possible_ids here.
Might be that not many drivers fill this out correctly, and in case fixing
that is much work, perhaps as a follow-up. But would be good to at least
help look down that part of uapi a bit more.

This isn't checked within atomic and legacy helpers since we assume that
->best_encoder respectively ->atomic_best_encoder gives us a valid encoder
...

> +
> +		drm_for_each_crtc(crtc, dev) {
> +			const struct drm_crtc_helper_funcs *crtc_funcs;
> +
> +			if (!drm_encoder_crtc_ok(encoder, crtc))
> +				continue;

We check this one here already in both atomic and legacy helpers, so all
drivers should get this right.

> +
> +			crtc_funcs = crtc->helper_private;
> +			if (!crtc_funcs || !crtc_funcs->mode_valid)
> +				return MODE_OK; /* crtc accepts everything */
> +
> +			ret = crtc_funcs->mode_valid(crtc, mode);
> +			if (ret == MODE_OK)
> +				/* If we get to this point there is at least
> +				 * one combination of encoder+crtc that works
> +				 * for this mode. Lets return now. */
> +				return ret;
> +		}
> +	}
> +
> +	return ret;
> +}
> +
>  static int drm_helper_probe_add_cmdline_mode(struct drm_connector *connector)
>  {
>  	struct drm_cmdline_mode *cmdline_mode;
> @@ -283,8 +344,10 @@ void drm_kms_helper_poll_enable(struct drm_device *dev)
>   *      (if specified)
>   *    - drm_mode_validate_flag() checks the modes against basic connector
>   *      capabilities (interlace_allowed,doublescan_allowed,stereo_allowed)
> - *    - the optional &drm_connector_helper_funcs.mode_valid helper can perform
> - *      driver and/or hardware specific checks
> + *    - the optional &drm_connector_helper_funcs.mode_valid,
> + *    	&drm_crtc_helper_funcs.mode_valid and
> + *    	&drm_encoder_helper_funcs.mode_valid helpers can perform driver and/or
> + *    	hardware specific checks

I'd leave 2 bullets for connector->mode_valid (sink specific checks) and
everything else (source checks, which are also enforced by the
modeset/atomic helpers).
>   *
>   * 5. Any mode whose status is not OK is pruned from the connector's modes list,
>   *    accompanied by a debug message indicating the reason for the mode's
> @@ -428,8 +491,8 @@ int drm_helper_probe_single_connector_modes(struct drm_connector *connector,
>  		if (mode->status == MODE_OK)
>  			mode->status = drm_mode_validate_flag(mode, mode_flags);
>  
> -		if (mode->status == MODE_OK && connector_funcs->mode_valid)
> -			mode->status = connector_funcs->mode_valid(connector,
> +		if (mode->status == MODE_OK)
> +			mode->status = drm_mode_validate_connector(connector,
>  								   mode);
>  	}
>  
> -- 
> 1.9.1
> 
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch