USB PHY documentation

[Martin Blumenstingl]

On Sat, Aug 27, 2016 at 11:32 PM, Martin Blumenstingl
<martin.blumenstingl at googlemail.com> wrote:
> On Fri, Aug 26, 2016 at 12:55 PM, Jérôme Brunet <jbrunet at baylibre.com> wrote:
>> I did some test on the otg controller. I had to remove the reset in the PHY
>> because it was reseting both of them, so the reset intended for the 2nd PHY
>> was breaking the configuration of the 1st.
> I am getting the following error when 1) removing the reset and 2)
> booting the mainline kernel directly (without booting the stock
> Android kernel first):
> [    1.297507] dwc2 c9000000.usb-controller: dwc2_core_reset() HANG!
> AHB Idle GRSTCTL=0
> [    1.305116] dwc2 c9000000.usb-controller: Bad value for GSNPSID: 0x00000000
I added the reset back along with some code that ensures it only calls
the reset once.
That made the error go away on my board.

Additionally I forced the first USB controller to "host" mode (which
was also not working without the reset) due to the OTG problems you
have mentioned.
I did some basic tests with both USB controllers - everything looks good!
While doing that I found out that quite a lot bits in REG_ADP_BC are
readonly - one of them is REG_ADP_BC_DRV_VBUS so I removed the code
which set that bit.

Finally I added our signed-off-by's to the patches and improved the
patch subjects and descriptions.
You can find my updated tree here: [0] (or if you only care about the
USB patches: [1])

PS: I will only have limited access to my S905 device in the next two weeks.
Feel free to submit the patches once you think they are ready - having
USB (host) support in 4.9 would be awesome!


Regards,
Martin


[0] https://github.com/xdarklight/linux/commits/meson-gxbb-integration-4.8-20160827
[1] https://github.com/torvalds/linux/compare/0ff577bf040b312301920f8589fc9fcea84a86b8...6aebadf13dcfb631399e7717c5eec0e80d72c9a7