Re: [Intel-gfx] [PATCH v1 06/13] drm/probe-helper: make .get_modes() optional, add default action

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Tue, May 24, 2022 at 01:39:28PM +0300, Jani Nikula wrote:
> Add default action when .get_modes() not set. This also defines what a
> .get_modes() hook should do.
> 
> Cc: David Airlie <airlied@linux.ie>
> Cc: Daniel Vetter <daniel@ffwll.ch>
> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
> ---
>  drivers/gpu/drm/drm_probe_helper.c       | 14 +++++++++++++-
>  include/drm/drm_modeset_helper_vtables.h |  4 ++++
>  2 files changed, 17 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_probe_helper.c b/drivers/gpu/drm/drm_probe_helper.c
> index 836bcd5b4cb6..9df17f0ae225 100644
> --- a/drivers/gpu/drm/drm_probe_helper.c
> +++ b/drivers/gpu/drm/drm_probe_helper.c
> @@ -360,7 +360,19 @@ static int drm_helper_probe_get_modes(struct drm_connector *connector)
>  		connector->helper_private;
>  	int count;
>  
> -	count = connector_funcs->get_modes(connector);
> +	if (connector_funcs->get_modes) {
> +		count = connector_funcs->get_modes(connector);
> +	} else {
> +		const struct drm_edid *drm_edid;
> +
> +		/* Note: This requires connector->ddc is set */
> +		drm_edid = drm_edid_read(connector);
> +
> +		/* Update modes etc. from the EDID */
> +		count = drm_edid_connector_update(connector, drm_edid);
> +
> +		drm_edid_free(drm_edid);
> +	}

Not really a huge fan of this automagic fallback. I think I'd prefer
to keep it mandatory and just provide this as a helper for drivers to
plug into the right spot. Otherwise I'm sure I'll forget how this works
and then I'll be confused when I see a connector withput any apparent
.get_modes() implementation.

>  
>  	/*
>  	 * Fallback for when DDC probe failed in drm_get_edid() and thus skipped
> diff --git a/include/drm/drm_modeset_helper_vtables.h b/include/drm/drm_modeset_helper_vtables.h
> index fafa70ac1337..b4402bc64e57 100644
> --- a/include/drm/drm_modeset_helper_vtables.h
> +++ b/include/drm/drm_modeset_helper_vtables.h
> @@ -894,6 +894,10 @@ struct drm_connector_helper_funcs {
>  	 * libraries always call this with the &drm_mode_config.connection_mutex
>  	 * held. Because of this it's safe to inspect &drm_connector->state.
>  	 *
> +	 * This callback is optional. By default, it reads the EDID using
> +	 * drm_edid_read() and updates the connector display info, modes, and
> +	 * properties using drm_edid_connector_update().
> +	 *
>  	 * RETURNS:
>  	 *
>  	 * The number of modes added by calling drm_mode_probed_add().
> -- 
> 2.30.2

-- 
Ville Syrjälä
Intel