FROMLIST: phy: rockchip-typec: Set the AUX channel flip state earlier
On some DP monitors we found that setting the wrong flip state on the
AUX channel could cause the monitor to stop asserting HotPlug Detect
(HPD). Setting the right flip state caused these monitors to start
asserting HotPlug Detect again.
Here's what we believe was happening:
* We'd plug in the monitor and we'd see HPD assert
* We'd quickly see HPD deassert
* The kernel would try to init the type C PHY but would init it in USB
mode (because there was a peripheral there but no HPD)
* Because the kernel never set the flip mode properly we'd never see
the HPD come back.
With this change, we'll still see HPD disappear (we don't think
there's anything we can do about that), but then it will come back.
Overall we can say that it's sane to set the AUX channel flip state
even when HPD is not asserted.
NOTE: to make this change possible, I needed to do a bit of cleanup to
the tcphy_dp_aux_calibration() function so that it doesn't ever
clobber the FLIP state. This made it very obvious that a line of code
documented as "setting bit 12" also did a bunch of other magic,
undocumented stuff. For now I'll just break out the bits and add a
comment that this is black magic and we'll try to document
tcphy_dp_aux_calibration() better in a future CL.
ALSO NOTE: the old function used to write a bunch of hardcoded
values in _some_ cases instead of doing a read-modify-write. One
could possibly assert that these could have had (beneficial) side
effects and thus with this new code (which always does
read-modify-write) we could have a bug. We shouldn't need to worry,
though, since in the old code tcphy_dp_aux_calibration() was always
called following the de-assertion of "reset" the the type C PHY.
...so the type C PHY was always in default state. TX_ANA_CTRL_REG_1
is documented to be 0x0 after reset. This was also confirmed by
TEST=Both orientations of DP cable with HP ZR30w work
Suggested-by: Shawn Nematbakhsh <email@example.com>
Reviewed-by: Chris Zhong <firstname.lastname@example.org>
Signed-off-by: Douglas Anderson <email@example.com>
(am from https://patchwork.kernel.org/patch/9941299/)
Reviewed-by: Guenter Roeck <firstname.lastname@example.org>
1 file changed