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Bind / unbind stress testing of the USB controller on rk3399 found that we'd often end up with lots of failures that looked like this: phy phy-ff800000.phy.9: phy poweron failed --> -110 dwc3 fe900000.dwc3: failed to initialize core dwc3: probe of fe900000.dwc3 failed with error -110 Those errors were sometimes seen at bootup too, in which case USB peripherals wouldn't work until unplugged and re-plugged in. I spent some time trying to figure out why the PHY was failing to power on but I wasn't able to. Possibly this has to do with the fact that the PHY docs say that the USB controller "needs to be held in reset to hold pipe power state in P2 before initializing the Type C PHY" but that doesn't appear to be easy to do with the dwc3 driver today. Messing around with the ordering of the reset vs. the PHY initialization in the dwc3 driver didn't seem to fix things. I did, however, find that if I simply retry the power on it seems to have a good chance of working. So let's add some retries. I ran a pretty tight bind/unbind loop overnight. When I did so, I found that I need to retry between 1% and 2% of the time. Overnight I found only a small handful of times where I needed 2 retries. I never found a case where I needed 3 retries. I'm completely aware of the fact that this is quite an ugly hack and I wish I didn't have to resort to it, but I have no other real idea how to make this hardware reliable. If Rockchip in the future can come up with a solution we can always revert this hack. Until then, let's at least have something that works. This patch is tested atop Enric's latest dwc3 patch series ending at: https://patchwork.kernel.org/patch/10095527/ ...but it could be applied independently of that series without any bad effects. For some more details on this bug, you can refer to: https://bugs.chromium.org/p/chromium/issues/detail?id=783464 Change-Id: I7909731247739694f56bf89ab3064889f2b34d3c Signed-off-by: Douglas Anderson <dianders@chromium.org> Signed-off-by: William Wu <william.wu@rock-chips.com> (am from https://patchwork.kernel.org/patch/10105833/)
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.
See Documentation/00-INDEX for a list of what is contained in each file.
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.