phy: rockchip-typec: Avoid magic numbers + add delays in aux calib

phy: rockchip-typec: Avoid magic numbers + add delays in aux calib

NOTE: nothing is known to be fixed by this change, but it does enforce
some delays that are documented to be necessary.  Possibly this could
fix some corner cases.

The function tcphy_dp_aux_calibration(), like most of the functions in
the type C PHY, is mostly undocumented and filled with mysterious,
hardcoded numbers.

Let's attempt to try to document some of these numbers and clean the
function up a little bit.  Here's the actual cleanup that happened
here:

1. All magic numbers were replaced with bit definitions.

2. For registers that we modify multiple times I now keep track of the
   value of the register rather than randomly doing a
   read/modify/write or just hardcoding a new number based on knowing
   what the old number was.

3. Delay 10 ms (vs 1 ms) after writing the calibration code.  No idea
   if this is important but it matches the example in the docs.

4. Whenever setting a "delayed" version of a signal always put an
   explicit delay in the code.  No known problems were seen without
   this delay but it seems wise to have it.  Whenever a delay of "at
   least 100 ns" was specified I used a delay of 1 us.

5. Added comments to some of the bits of code.

6. Removed duplicate setting of TX_ANA_CTRL_REG_5 (to 0)

7. Moved setting of TX_ANA_CTRL_REG_3 to the same place it was in the
   sample code.  Note that TX_ANA_CTRL_REG_3 ought to be initted to 0
   (and elsewhere we assume that we just got a reset), but it seems
   fine to be explicit.

8. Treats the calibration code as a 7-bit two's complement number.
   This isn't strictly required, but seems slightly cleaner.  The docs
   say "treat this as a two's complement number, but it should never
   be negative".  If we ever read the "adjustment" codes as documented
   then perhaps the two's complement bit will matter more.

There are still a few weird / mysterious things around aux init and
this doesn't attempt to fix all of them.  Mostly it's aimed at doing
changes that should be _very_ safe and add a lot of clarity.  Things
specifically not done:

A) Resolve the fact that some registers are read/modify/write and
   others are explicitly initted to a value.  We always call
   tcphy_dp_aux_calibration() right after resetting the PHY so it's
   probably not critical, but it's a little weird that the code is
   inconsistent.

B) Fully resolve the documented init sequence with the current one.
   We still have a few mystery steps and we also leave out turning on
   TXDA_DRV_LDO_BG_FB_EN and TXDA_DRV_LDO_BG_REF_EN, which is in the
   sample code.

C) Clean things up to read all the bits of the calibration code.  This
   will hopefully come in a followup change.

This also doesn't attempt to document any of the other parts of the
PHY--just the aux init which is all I got docs for.

Reviewed-by: Chris Zhong <zyw@rock-chips.com>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>