Re: [PATCH v3 2/2] drm/fb-helper: pass physical dimensions to fbdev

[Daniel Vetter]

On Thu, Aug 03, 2017 at 11:19:09AM -0500, David Lechner wrote:
> The fbdev subsystem has a place for physical dimensions (width and height
> in mm) that is readable by userspace. Since DRM also knows these
> dimensions, pass this information to the fbdev device.
> 
> This has to be done in drm_setup_crtcs_fb() instead of drm_setup_crtcs()
> because fb_helper->fbdev may be NULL in drm_setup_crtcs().
> 
> Signed-off-by: David Lechner <david@xxxxxxxxxxxxxx>
> ---
>  drivers/gpu/drm/drm_fb_helper.c | 15 +++++++++++++--
>  1 file changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> index 24a721a..a98bf86 100644
> --- a/drivers/gpu/drm/drm_fb_helper.c
> +++ b/drivers/gpu/drm/drm_fb_helper.c
> @@ -1882,8 +1882,6 @@ void drm_fb_helper_fill_var(struct fb_info *info, struct drm_fb_helper *fb_helpe
>  	info->var.xoffset = 0;
>  	info->var.yoffset = 0;
>  	info->var.activate = FB_ACTIVATE_NOW;
> -	info->var.height = -1;
> -	info->var.width = -1;
>  
>  	switch (fb->format->depth) {
>  	case 8:
> @@ -2435,11 +2433,24 @@ static void drm_setup_crtcs(struct drm_fb_helper *fb_helper,
>   */
>  static void drm_setup_crtcs_fb(struct drm_fb_helper *fb_helper)
>  {
> +	struct fb_info *info = fb_helper->fbdev;
>  	int i;
>  
>  	for (i = 0; i < fb_helper->crtc_count; i++)
>  		if (fb_helper->crtc_info[i].mode_set.num_connectors)
>  			fb_helper->crtc_info[i].mode_set.fb = fb_helper->fb;
> +
> +	drm_fb_helper_for_each_connector(fb_helper, i) {
> +		struct drm_connector *connector =
> +					fb_helper->connector_info[i]->connector;
> +
> +		/* use first connected connector for the physical dimensions */
> +		if (connector->status == connector_status_connected) {
> +			info->var.height = connector->display_info.width_mm;
> +			info->var.width = connector->display_info.height_mm;
> +			break;
> +		}
> +	}

Ok, small trapdoor I didn't highlight: Accessing the connector prope state
(i.e. ->status and ->display_info) requires that you hold
dev->mode_config.mutex. See how it's done in drm_setup_crtcs, just wrap it
around this loop here.

fbdev state itself is protected by fb_helper->lock, so that part is all
good.

I've applied patch 1 already, but can you pls respin that one with the
locking fixed up?

Thanks, Daniel
>  }
>  
>  /* Note: Drops fb_helper->lock before returning. */
> -- 
> 2.7.4
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch