On 16/11/18 01:06, Sebastian Reichel wrote:
> The DSI encoder sets dssdev->ops->dsi.set_config, which is stored at the
> same offset as dssdev->ops->hdmi.set_hdmi_mode. The code in omap_encoder
> only checks if dssdev->ops->hdmi.set_hdmi_mode is NULL. Due to the way
> union works, it won't be NULL if dsi.set_config is set. This means
> dsi_set_config will be called with config=hdmi_mode=false=NULL parameter
> resulting in a NULL dereference. Also the dereference happens while
> console is locked, so kernel hangs without any debug output (can be
> avoided by fbmem's lockless_register_fb=1 parameter).
>
> This fixes the issue by exiting early if the output type definitely
> has no hdmi_set operations.
>
> Fixes: 83910ad3f51fb ("drm/omap: Move most omap_dss_driver operations to
> omap_dss_device_ops")
> Signed-off-by: Sebastian Reichel <sebastian.reic...@collabora.com>
> ---
> drivers/gpu/drm/omapdrm/omap_encoder.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/drivers/gpu/drm/omapdrm/omap_encoder.c
> b/drivers/gpu/drm/omapdrm/omap_encoder.c
> index 32bbe3a80e7d..ba0099f0644c 100644
> --- a/drivers/gpu/drm/omapdrm/omap_encoder.c
> +++ b/drivers/gpu/drm/omapdrm/omap_encoder.c
> @@ -122,6 +122,14 @@ static void omap_encoder_mode_set(struct drm_encoder
> *encoder,
>
> dssdev = omap_encoder->output;
>
> + /* The following operations access dssdev->ops->hdmi, which is a union
> + * also used by DSI. This ensures, that the field does not have data
> + * for DSI (or any other future output type).
> + */
> + if (dssdev->output_type != OMAP_DISPLAY_TYPE_HDMI &&
> + dssdev->output_type != OMAP_DISPLAY_TYPE_DVI)
Good catch.
Why DVI?
I think the whole code block starting from
/* Set the HDMI mode and HDMI infoframe if applicable. */
to the end of the function should be inside
if (dssdev->output_type == OMAP_DISPLAY_TYPE_HDMI)
Tomi
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