b7563e2796
Stefan Wahren reports a problem with a warning fix that was merged for v4.15: we had lots of device nodes with a 'phys' property pointing to a device node that is not compliant with the binding documented in Documentation/devicetree/bindings/phy/phy-bindings.txt This generally works because USB HCD drivers that support both the generic phy subsystem and the older usb-phy subsystem ignore most errors from phy_get() and related calls and then use the usb-phy driver instead. However, it turns out that making the usb-nop-xceiv device compatible with the generic-phy binding changes the phy_get() return code from -EINVAL to -EPROBE_DEFER, and the dwc2 usb controller driver for bcm2835 now returns -EPROBE_DEFER from its probe function rather than ignoring the failure, breaking all USB support on raspberry-pi when CONFIG_GENERIC_PHY is enabled. The same code is used in the dwc3 driver and the usb_add_hcd() function, so a reasonable assumption would be that many other platforms are affected as well. I have reviewed all the related patches and concluded that "usb-nop-xceiv" is the only USB phy that is affected by the change, and since it is by far the most commonly referenced phy, all the other USB phy drivers appear to be used in ways that are are either safe in DT (they don't use the 'phys' property), or in the driver (they already ignore -EPROBE_DEFER from generic-phy when usb-phy is available). To work around the problem, this adds a special case to _of_phy_get() so we ignore any PHY node that is compatible with "usb-nop-xceiv", as we know that this can never load no matter how much we defer. In the future, we might implement a generic-phy driver for "usb-nop-xceiv" and then remove this workaround. Since we generally want older kernels to also want to work with the fixed devicetree files, it would be good to backport the patch into stable kernels as well (3.13+ are possibly affected), even though they don't contain any of the patches that may have caused regressions. Fixes: |
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README
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. 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.