linux-kernel - Re: [PATCH v5] drm/fb-helper: pass physical dimensions to fbdev

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Date:   Sat, 05 Aug 2017 00:53:35 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     dri-devel@...ts.freedesktop.org
Cc:     David Lechner <david@...hnology.com>, linux-kernel@...r.kernel.org,
        Daniel Vetter <daniel.vetter@...el.com>
Subject: Re: [PATCH v5] drm/fb-helper: pass physical dimensions to fbdev

Hi David,

Thank you for the patch.

On Friday 04 Aug 2017 11:25:24 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.

I'm curious, what's your use case for this ? What userspace software do you 
use that is still based on fbdev and needs screen dimensions ?

> 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().
> ---
> 
> v1 changes (from RFC):
> * Use loop to get info from first connected connector instead of just the
>   first connector.
> 
> v2 changes:
> * Update width in height in drm_setup_crtcs() also to handle hotplug events.
> 
> v3 changes:
> * Add new patch to handle post-fb allocation crcts setup.
> * Use new drm_setup_crtcs_fb() function from new patch to avoid duplication
>   of code.
> 
> v4 changes:
> * Drop patch "drm/fb-helper: add new drm_setup_crtcs_fb() function" since it
> has been applied already.
> * Add mutex lock.
> 
> v5 changes:
> * Fix height = width mismatch.
> 
>  drivers/gpu/drm/drm_fb_helper.c | 17 +++++++++++++++--
>  1 file changed, 15 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_fb_helper.c
> b/drivers/gpu/drm/drm_fb_helper.c index 4447a28..24787d6 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 +2433,26 @@ 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;
> +
> +	mutex_lock(&fb_helper->dev->mode_config.mutex);
> +	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.width = connector->display_info.width_mm;
> +			info->var.height = connector-
>display_info.height_mm;
> +			break;
> +		}
> +	}
> +	mutex_unlock(&fb_helper->dev->mode_config.mutex);
>  }
> 
>  /* Note: Drops fb_helper->lock before returning. */

-- 
Regards,

Laurent Pinchart