[PATCH] compositor-drm: consider the best mode of the mode_list as an option

[Bryce W. Harrington]

On Thu, Dec 12, 2013 at 05:13:56PM +0100, Fabien DESSENNE wrote:
> This patch fixes an issue where Weston using the DRM backend, cannot start
> the display. This happens in the following context:
> - no video mode is set before weston starts (eg no "/dev/fb" set up)
> - weston is not configured with any default video mode (nothing from
>   weston.ini nor command line)
> - the DRM driver provides with a list of supported modes, but none of them
>   is marked as PREFERRED (which is not a usual case, but it happens)

Good point, I've seen such hardware myself.

> In that case, according to the current implementation, the DRM compositor
> fails to set a video mode.
> This fix lets the DRM compositor selects a video mode (the best one of the
> list, which is the first) from the ones provided by the driver.

Is it always guaranteed to be the best, or is it just returning the list
in the order stored in EDID?  Either way, picking the first in the list
is probably sensible, however in the latter case I don't know that we
can assume it's the 'best'.  Maybe the variable should be called 'first'
rather than 'best'?  But I'm just bikeshedding...
 
> Signed-off-by: Fabien Dessenne <fabien.dessenne at st.com>

Reviewed-by: Bryce Harrington <b.harrington at samsung.com>

> ---
>  src/compositor-drm.c |    6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/src/compositor-drm.c b/src/compositor-drm.c
> index fbf6e49..54caaa9 100644
> --- a/src/compositor-drm.c
> +++ b/src/compositor-drm.c
> @@ -1858,7 +1858,7 @@ create_output_for_connector(struct drm_compositor *ec,
>  			    int x, int y, struct udev_device *drm_device)
>  {
>  	struct drm_output *output;
> -	struct drm_mode *drm_mode, *next, *preferred, *current, *configured;
> +	struct drm_mode *drm_mode, *next, *preferred, *current, *configured, *best;
>  	struct weston_mode *m;
>  	struct weston_config_section *section;
>  	drmModeEncoder *encoder;
> @@ -1961,6 +1961,7 @@ create_output_for_connector(struct drm_compositor *ec,
>  	preferred = NULL;
>  	current = NULL;
>  	configured = NULL;
> +	best = NULL;
>  
>  	wl_list_for_each_reverse(drm_mode, &output->base.mode_list, base.link) {
>  		if (config == OUTPUT_CONFIG_MODE &&
> @@ -1971,6 +1972,7 @@ create_output_for_connector(struct drm_compositor *ec,
>  			current = drm_mode;
>  		if (drm_mode->base.flags & WL_OUTPUT_MODE_PREFERRED)
>  			preferred = drm_mode;
> +		best = drm_mode;
>  	}
>  
>  	if (config == OUTPUT_CONFIG_MODELINE) {
> @@ -1996,6 +1998,8 @@ create_output_for_connector(struct drm_compositor *ec,
>  		output->base.current_mode = &preferred->base;
>  	else if (current)
>  		output->base.current_mode = &current->base;
> +	else if (best)
> +		output->base.current_mode = &best->base;
>  
>  	if (output->base.current_mode == NULL) {
>  		weston_log("no available modes for %s\n", output->base.name);
> -- 
> 1.7.9.5
> 
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