[PATCH] drm/fbdev: Clamp fbdev surface size if too large

[Ville Syrjälä]

On Mon, Oct 04, 2021 at 10:15:06AM +0200, Thomas Zimmermann wrote:
> Clamp the fbdev surface size of the available maximum height to avoid
> failing to init console emulation. An example error is shown below.
> 
>   bad framebuffer height 2304, should be >= 768 && <= 768
>   [drm] Initialized simpledrm 1.0.0 20200625 for simple-framebuffer.0 on minor 0
>   simple-framebuffer simple-framebuffer.0: [drm] *ERROR* fbdev: Failed to setup generic emulation (ret=-22)
> 
> This is especially a problem with drivers that have very small screen
> sizes and cannot over-allocate at all.
> 
> Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
> Fixes: 11e8f5fd223b ("drm: Add simpledrm driver")
> Reported-by: Amanoel Dawod <kernel at amanoeldawod.com>
> Reported-by: Zoltán Kővágó <dirty.ice.hu at gmail.com>
> Reported-by: Michael Stapelberg <michael+lkml at stapelberg.ch>
> Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
> Cc: Maxime Ripard <maxime at cerno.tech>
> Cc: dri-devel at lists.freedesktop.org
> Cc: <stable at vger.kernel.org> # v5.14+
> ---
>  drivers/gpu/drm/drm_fb_helper.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> index 6860223f0068..364f11900b37 100644
> --- a/drivers/gpu/drm/drm_fb_helper.c
> +++ b/drivers/gpu/drm/drm_fb_helper.c
> @@ -1508,6 +1508,7 @@ static int drm_fb_helper_single_fb_probe(struct drm_fb_helper *fb_helper,
>  {
>  	struct drm_client_dev *client = &fb_helper->client;
>  	struct drm_device *dev = fb_helper->dev;
> +	struct drm_mode_config *config = &dev->mode_config;
>  	int ret = 0;
>  	int crtc_count = 0;
>  	struct drm_connector_list_iter conn_iter;
> @@ -1665,6 +1666,11 @@ static int drm_fb_helper_single_fb_probe(struct drm_fb_helper *fb_helper,
>  	/* Handle our overallocation */
>  	sizes.surface_height *= drm_fbdev_overalloc;
>  	sizes.surface_height /= 100;
> +	if (sizes.surface_height > config->max_height) {
> +		drm_warn(dev, "Fbdev over-allocation too large; clamping height to %d\n",
> +			 config->max_height);

drm_warn() seems a bit excessive. drm_info()?

Or could just have no printk and use a simple min() perhaps.

> +		sizes.surface_height = config->max_height;
> +	}
> 
>  	/* push down into drivers */
>  	ret = (*fb_helper->funcs->fb_probe)(fb_helper, &sizes);
> --
> 2.33.0

-- 
Ville Syrjälä
Intel