forked from Minki/linux
40ee6fbef7
At the time userspace does setcrtc, we've already promised the mode would work. The promise is based on the theoretical capabilities of the link, but it's possible we can't reach this in practice. The DP spec describes how the link should be reduced, but we can't reduce the link below the requirements of the mode. Black screen follows. One idea would be to have setcrtc return a failure. However, it already should not fail as the atomic checks have passed. It would also conflict with the idea of making setcrtc asynchronous in the future, returning before the actual mode setting and link training. Another idea is to train the link "upfront" at hotplug time, before pruning the mode list, so that we can do the pruning based on practical not theoretical capabilities. However, the changes for link training are pretty drastic, all for the sake of error handling and DP compliance, when the most common happy day scenario is the current approach of link training at mode setting time, using the optimal parameters for the mode. It is also not certain all hardware could do this without the pipe on; not even all our hardware can do this. Some of this can be solved, but not trivially. Both of the above ideas also fail to address link degradation *during* operation. The solution is to add a new "link-status" connector property in order to address link training failure in a way that: a) changes the current happy day scenario as little as possible, to avoid regressions, b) can be implemented the same way by all drm drivers, c) is still opt-in for the drivers and userspace, and opting out doesn't regress the user experience, d) doesn't prevent drivers from implementing better or alternate approaches, possibly without userspace involvement. And, of course, handles all the issues presented. In the usual happy day scenario, this is always "good". If something fails during or after a mode set, the kernel driver can set the link status to "bad" and issue a hotplug uevent for userspace to have it re-check the valid modes through GET_CONNECTOR IOCTL, and try modeset again. If the theoretical capabilities of the link can't be reached, the mode list is trimmed based on that. v7 by Jani: * Rebase, simplify set property while at it, checkpatch fix v6: * Fix a typo in kernel doc (Sean Paul) v5: * Clarify doc for silent rejection of atomic properties by driver (Daniel Vetter) v4: * Add comments in kernel-doc format (Daniel Vetter) * Update the kernel-doc for link-status (Sean Paul) v3: * Fixed a build error (Jani Saarinen) v2: * Removed connector->link_status (Daniel Vetter) * Set connector->state->link_status in drm_mode_connector_set_link_status_property (Daniel Vetter) * Set the connector_changed flag to true if connector->state->link_status changed. * Reset link_status to GOOD in update_output_state (Daniel Vetter) * Never allow userspace to set link status from Good To Bad (Daniel Vetter) Reviewed-by: Sean Paul <seanpaul@chromium.org> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch> Reviewed-by: Jani Nikula <jani.nikula@intel.com> Acked-by: Tony Cheng <tony.cheng@amd.com> Acked-by: Harry Wentland <harry.wentland@amd.com> Cc: Jani Nikula <jani.nikula@linux.intel.com> Cc: Daniel Vetter <daniel.vetter@intel.com> Cc: Ville Syrjala <ville.syrjala@linux.intel.com> Cc: Chris Wilson <chris@chris-wilson.co.uk> Cc: Sean Paul <seanpaul@chromium.org> Signed-off-by: Manasi Navare <manasi.d.navare@intel.com> Signed-off-by: Jani Nikula <jani.nikula@intel.com> Acked-by: Eric Anholt <eric@anholt.net> (for the -modesetting patch) Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch> Link: http://patchwork.freedesktop.org/patch/msgid/0182487051aa9f1594820e35a4853de2f8747b4e.1481883920.git.jani.nikula@intel.com |
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