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Douglas Anderson a70e558c15 drm/bridge: ti-sn65dsi86: Don't read EDID blob over DDC 
This is really just a revert of commit 58074b08c0 ("drm/bridge:
ti-sn65dsi86: Read EDID blob over DDC"), resolving conflicts.

The old code failed to read the EDID properly in a very important
case: before the bridge's pre_enable() was called. The way things need
to work:
1. Read the EDID.
2. Based on the EDID, decide on video settings and pixel clock.
3. Enable the bridge w/ the desired settings.

The way things were working:
1. Try to read the EDID but fail; fall back to hardcoded values.
2. Based on hardcoded values, decide on video settings and pixel clock.
3. Enable the bridge w/ the desired settings.
4. Try again to read the EDID, it works now!
5. Realize that the hardcoded settings weren't quite right.
6. Disable / reenable the bridge w/ the right settings.

The reasons for the failures were twofold:
a) Since we never ran the bridge chip's pre-enable then we never set
   the bit to ignore HPD. This meant the bridge chip didn't even _try_
   to go out on the bus and communicate with the panel.
b) Even if we fixed things to ignore HPD, the EDID still wouldn't read
   if the panel wasn't on.

Instead of reverting the code, we could fix it to set the HPD bit and
also power on the panel. However, it also works nicely to just let the
panel code read the EDID. Now that we've split the driver up we can
expose the DDC AUX channel bus to the panel node. The panel can take
charge of reading the EDID.

NOTE: in order for things to work, anyone that needs to read the EDID
will need to instantiate their panel using the new DP AUX bus (AKA by
listing their panel under the "aux-bus" node of the bridge chip in the
device tree).

In the future if we want to use the bridge chip to provide a full
external DP port (which won't have a panel) then we will have to
conditinally add EDID reading back in.

Suggested-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20210611101711.v10.9.I9330684c25f65bb318eff57f0616500f83eac3cc@changeid
2021-06-11 12:31:45 -07:00
arch Cross-subsystem Changes: 2021-06-10 13:45:11 +10:00
block block-5.13-2021-05-22 2021-05-22 07:40:34 -10:00
certs Kbuild updates for v5.13 (2nd) 2021-05-08 10:00:11 -07:00
crypto
Documentation dt-bindings: drm/bridge: ti-sn65dsi86: Add aux-bus child 2021-06-11 12:29:42 -07:00
drivers drm/bridge: ti-sn65dsi86: Don't read EDID blob over DDC 2021-06-11 12:31:45 -07:00
fs userfaultfd: hugetlbfs: fix new flag usage in error path 2021-05-22 15:09:07 -10:00
include drm: Introduce the DP AUX bus 2021-06-11 12:30:39 -07:00
init Merge branch 'akpm' (patches from Andrew) 2021-05-07 00:34:51 -07:00
ipc ipc/mqueue, msg, sem: avoid relying on a stack reference past its expiry 2021-05-22 15:09:07 -10:00
kernel Two locking fixes: 2021-05-23 06:30:08 -10:00
lib lib: kunit: suppress a compilation warning of frame size 2021-05-22 15:09:07 -10:00
LICENSES
mm userfaultfd: hugetlbfs: fix new flag usage in error path 2021-05-22 15:09:07 -10:00
net Char/misc driver fixes for 5.13-rc3 2021-05-20 06:31:52 -10:00
samples Kbuild updates for v5.13 (2nd) 2021-05-08 10:00:11 -07:00
scripts kbuild: dummy-tools: adjust to stricter stackprotector check 2021-05-17 12:10:03 +09:00
security trusted-keys: match tpm_get_ops on all return paths 2021-05-12 22:36:37 +03:00
sound sound fixes for 5.13-rc3 2021-05-20 06:42:21 -10:00
tools powerpc fixes for 5.13 #4 2021-05-23 06:07:33 -10:00
usr
virt kvm: Cap halt polling at kvm->max_halt_poll_ns 2021-05-07 06:06:22 -04:00
.clang-format
.cocciconfig
.get_maintainer.ignore
.gitattributes
.gitignore
.mailmap Merge drm/drm-fixes into drm-misc-fixes 2021-05-11 13:35:52 +02:00
COPYING
CREDITS
Kbuild
Kconfig
MAINTAINERS drm/panel: db7430: Add driver for Samsung DB7430 2021-06-11 00:43:45 +02:00
Makefile Linux 5.13-rc3 2021-05-23 11:42:48 -10:00
README

README 

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.