9e15123eca
In commit7d8e9a9050("drm/msm/dsi: move DSI host powerup to modeset time"), we moved powering up DSI hosts to modeset time. This wasn't because it was an elegant design, but there were no better options. That commit actually ended up breaking ps8640, and thus was born commitec7981e6c6("drm/msm/dsi: don't powerup at modeset time for parade-ps8640") as a temporary hack to un-break ps8640 by moving it to the old way of doing things. It turns out that ps8640 _really_ doesn't like its pre_enable() function to be called after dsi_mgr_bridge_power_on(). Specifically (from experimentation, not because I have any inside knowledge), it looks like the assertion of "RST#" in the ps8640 runtime resume handler seems like it's not allowed to happen after dsi_mgr_bridge_power_on() Recently, Dave Stevenson's series landed allowing bridges some control over pre_enable ordering. The meaty commit for our purposes is commit4fb912e5e1("drm/bridge: Introduce pre_enable_prev_first to alter bridge init order"). As documented by that series, if a bridge doesn't set "pre_enable_prev_first" then we should use the old ordering. Now that we have the commit ("drm/bridge: tc358762: Set pre_enable_prev_first") we can go back to the old ordering, which also allows us to remove the ps8640 special case. One last note is that even without reverting commit7d8e9a9050("drm/msm/dsi: move DSI host powerup to modeset time"), if you _just_ revert the ps8640 special case and try it out then it doesn't seem to fail anymore. I spent time bisecting / debugging this and it turns out to be mostly luck, so we still want this patch to make sure it's solid. Specifically the reason it sorta works these days is because we implemented wait_hpd_asserted() in ps8640 now, plus the magic of "pm_runtime" autosuspend. The fact that we have wait_hpd_asserted() implemented means that we actually power the bridge chip up just a wee bit earlier and then the bridge happens to stay on because of autosuspend and thus ends up powered before dsi_mgr_bridge_power_on(). Cc: Dave Stevenson <dave.stevenson@raspberrypi.com> Cc: Dmitry Baryshkov <dmitry.baryshkov@linaro.org> Cc: Abhinav Kumar <quic_abhinavk@quicinc.com> Signed-off-by: Douglas Anderson <dianders@chromium.org> Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com> Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org> Patchwork: https://patchwork.freedesktop.org/patch/521058/ Link: https://lore.kernel.org/r/20230131141756.RFT.v2.2.I4cfeab9d0e07e98ead23dd0736ab4461e6c69002@changeid Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.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.