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

From: Daniel Vetter
Date: Fri Aug 04 2017 - 04:59:05 EST


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