Re: [PATCH 1/2] drm: Introduce crtc->mode_valid() callback

[Ville Syrjälä]

On Wed, Apr 26, 2017 at 11:48:34AM +0100, Jose Abreu wrote:
> Some crtc's may have restrictions in the mode they can display. In
> this patch a new callback (crtc->mode_valid()) is introduced that
> is called at the same stage of connector->mode_valid() callback.
> 
> This shall be implemented if the crtc has some sort of restriction
> so that we don't probe modes that will fail in the commit() stage.
> For example: A given crtc may be responsible to set a clock value.
> If the clock can not produce all the values for the available
> modes then this callback can be used to restrict the number of
> probbed modes to only the ones that can be displayed.
> 
> If the crtc does not implement the callback then the behaviour will
> remain the same. Also, for a given set of crtcs that can be bound to
> the connector, if at least one can display the mode then the mode
> will be probbed.
> 
> 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>
> ---
>  drivers/gpu/drm/drm_probe_helper.c       | 44 ++++++++++++++++++++++++++++++++
>  include/drm/drm_modeset_helper_vtables.h | 26 +++++++++++++++++++
>  2 files changed, 70 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_probe_helper.c b/drivers/gpu/drm/drm_probe_helper.c
> index 1b0c14a..61eac30 100644
> --- a/drivers/gpu/drm/drm_probe_helper.c
> +++ b/drivers/gpu/drm/drm_probe_helper.c
> @@ -80,6 +80,46 @@
>  	return MODE_OK;
>  }
>  
> +static enum drm_mode_status drm_mode_validate_connector_crtc(
> +		struct drm_connector *connector,
> +		struct drm_display_mode *mode)

Probably more typical way to split the lines would be:
static enum drm_mode_status
drm_mode_validate_connector_crtc(struct drm_connector *connector,
				 struct drm_display_mode *mode)

Also 'mode' should be const. Looks like the connector->mode_valid()
hook is missing the const as well, so that too should be fixed.

Not sure about the name of the function. It doesn't really reflect what
it does in the best way possible. drm_mode_validate_connector_possible_crtcs()
perhaps? But that is getting quite long so not sure if it' a good idea
either. I guess simply making the name refer to plural crtcs might be
a reasonable compromise, ie. drm_mode_validate_connector_crtcs()?

> +{
> +	const struct drm_crtc_helper_funcs *crtc_funcs = NULL;
> +	enum drm_mode_status mode_status = MODE_ERROR;
> +	struct drm_device *dev = connector->dev;
> +	struct drm_encoder *encoder;
> +	struct drm_crtc *crtc;

A lot of these can be moved into tighter scope.

> +	bool callback_found = false;

I don't think you need this variable at all. See below.

> +	int i;
> +
> +	for (i = 0; i < DRM_CONNECTOR_MAX_ENCODER; i++) {
> +		encoder = drm_encoder_find(dev, connector->encoder_ids[i]);
> +
> +		if (!encoder)
> +			continue;
> +
> +		drm_for_each_crtc(crtc, dev) {
> +			crtc_funcs = crtc->helper_private;
> +
> +			if (!drm_encoder_crtc_ok(encoder, crtc))
> +				continue;
> +			if (!crtc_funcs || !crtc_funcs->mode_valid)
> +				continue;
> +
> +			/* MODE_OK=0 and default mode_status=MODE_ERROR=-1
> +			 * so if at least one crtc accepts the mode we get
> +			 * MODE_OK */
> +			mode_status &= crtc_funcs->mode_valid(crtc, mode);
> +			callback_found |= true;

The need for a comment here tells me that it's probably better
to got for a more straightforward code. Something like:

mode_status = crtc_funcs->mode_valid(crtc, mode);
if (mode_statys == MODE_OK)
	return mode_status;

And at the end of the function just return MODE_ERROR, or
some other error value if we have something suitable. Hmm.
Perhaps we should just return the error from the first or last
crtc? Either should be pretty easy, just "ret = mode_status" within
the loop if it didn't return MODE_OK and then 'return ret' at the
end of the function.

> +		}
> +	}
> +
> +	/* We can reach here without calling mode_valid if there is no
> +	 * registered crtc with this callback, lets return MODE_OK in this
> +	 * case */
> +	return callback_found ? mode_status : MODE_OK;
> +}
> +
>  static int drm_helper_probe_add_cmdline_mode(struct drm_connector *connector)
>  {
>  	struct drm_cmdline_mode *cmdline_mode;
> @@ -431,6 +471,10 @@ int drm_helper_probe_single_connector_modes(struct drm_connector *connector,
>  		if (mode->status == MODE_OK && connector_funcs->mode_valid)
>  			mode->status = connector_funcs->mode_valid(connector,
>  								   mode);
> +
> +		if (mode->status == MODE_OK)
> +			mode->status = drm_mode_validate_connector_crtc(
> +					connector, mode);

Indentation.

And actually, maybe you should also move the connector_funcs->mode_valid()
call into the new function, and then you could just call the new
function drm_mode_validate_connector() or something along those lines.

>  	}
>  
>  prune:
> diff --git a/include/drm/drm_modeset_helper_vtables.h b/include/drm/drm_modeset_helper_vtables.h
> index c01c328..59fffba 100644
> --- a/include/drm/drm_modeset_helper_vtables.h
> +++ b/include/drm/drm_modeset_helper_vtables.h
> @@ -106,6 +106,32 @@ struct drm_crtc_helper_funcs {
>  	void (*commit)(struct drm_crtc *crtc);
>  
>  	/**
> +	 * @mode_valid:
> +	 *
> +	 * This callback should be implemented if the crtc has some sort of
> +	 * restriction in the modes it can display. For example, a given crtc
> +	 * may be responsible to set a clock value. If the clock can not
> +	 * produce all the values for the available modes then this callback
> +	 * can be used to restrict the number of probbed modes to only the ones
> +	 * that can be displayed.
> +	 *
> +	 * This is directly called at the same stage of connector->mode_valid
> +	 * callback.
> +	 *
> +	 * NOTE:
> +	 *
> +	 * For a given set of crtc's in a drm_device, if at least one does not
> +	 * have the mode_valid callback, or, at least one returns MODE_OK then
> +	 * the mode will be probbed.
> +	 *
> +	 * RETURNS:
> +	 *
> +	 * drm_mode_status Enum
> +	 */
> +	enum drm_mode_status (*mode_valid)(struct drm_crtc *crtc,
> +			struct drm_display_mode *mode);

Const. Indentation looks off again.

> +
> +	/**
>  	 * @mode_fixup:
>  	 *
>  	 * This callback is used to validate a mode. The parameter mode is the
> -- 
> 1.9.1
> 

-- 
Ville Syrjälä
Intel OTC