Pick user-defined display mode in DRM clients if the mode has been validated by the driver. Otherwise pick a preferred display mode.
Booting the kernel with video=<mode> and giving an unsupported display mode can easily turn the display unusable. This is best tested by booting simpledrm with a display mode that does not use the firmware framebuffer's resolution. While simpledrm filter's out the mode as invalid, the DRM client still picks it and the console won't show up.
Several factors contribute to this problem.
* The connector invalidates the user-defined display mode, but never tells the user about it. * The DRM client doesn't look for user-defined display modes, but for modes that are similar. * If no similar mode can be found, the client adds the invalid display mode back to the connector's mode list for use.
Each of the patches in this patchset addresses one of these problems. Overall the DRM client has no business in display-mode detection and should only pick one of the modes that has been detected and validated by the connector.
Thomas Zimmermann (3): drm: Always warn if user-defined modes are not supported drm/client: Look for command-line modes first drm/client: Don't add new command-line mode
drivers/gpu/drm/drm_client_modeset.c | 28 ++++++++++++++++------------ drivers/gpu/drm/drm_modes.c | 4 ++++ 2 files changed, 20 insertions(+), 12 deletions(-)