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commit 6c34bd4532a3f39952952ddc102737595729afc4 upstream. Atm, there are no sink rate values set for DP (vs. eDP) sinks until the DPCD capabilities are successfully read from the sink. During this time intel_dp->num_common_rates is 0 which can lead to a intel_dp->common_rates[-1] (*) access, which is an undefined behaviour, in the following cases: - In intel_dp_sync_state(), if the encoder is enabled without a sink connected to the encoder's connector (BIOS enabled a monitor, but the user unplugged the monitor until the driver loaded). - In intel_dp_sync_state() if the encoder is enabled with a sink connected, but for some reason the DPCD read has failed. - In intel_dp_compute_link_config() if modesetting a connector without a sink connected on it. - In intel_dp_compute_link_config() if modesetting a connector with a a sink connected on it, but before probing the connector first. To avoid the (*) access in all the above cases, make sure that the sink rate table - and hence the common rate table - is always valid, by setting a default minimum sink rate when registering the connector before anything could use it. I also considered setting all the DP link rates by default, so that modesetting with higher resolution modes also succeeds in the last two cases above. However in case a sink is not connected that would stop working after the first modeset, due to the LT fallback logic. So this would need more work, beyond the scope of this fix. As I mentioned in the previous patch, I don't think the issue this patch fixes is user visible, however it is an undefined behaviour by definition and triggers a BUG() in CONFIG_UBSAN builds, hence CC:stable. v2: Clear the default sink rates, before initializing these for eDP. Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/4297 References: https://gitlab.freedesktop.org/drm/intel/-/issues/4298 Suggested-by: Ville Syrjälä <ville.syrjala@linux.intel.com> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com> Cc: <stable@vger.kernel.org> Signed-off-by: Imre Deak <imre.deak@intel.com> Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com> Acked-by: Jani Nikula <jani.nikula@intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20211018143417.1452632-1-imre.deak@intel.com (cherry picked from commit 3f61ef9777c0ab0f03f4af0ed6fd3e5250537a8d) Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.