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The USB PHY on MSM8909 works with the driver used on MSM8916 (phy-qcom-usb-hs.c). When turning the PHY on/off it is first reset using the standard reset controller API. On MSM8916 the reset is provided by the USB driver (ci_hdrc_msm_por_reset() in ci_hdrc_msm.c). While this seems to work on MSM8909 as well, the Qualcomm Linux sources suggest that the PHY should be reset using the GCC_USB2_HS_PHY_ONLY_BCR register instead. In general this is easy to set up in the device tree, thanks to the standard reset controller API. However, to conform to the specifications of the PHY the reset signal should be asserted for at least 10 us. This is handled correctly on MSM8916 in ci_hdrc_msm_por_reset(), but not within the GCC driver. Fix this by making use of the new "udelay" field of qcom_reset_map and set a delay of ~15 us between the assertion/deassertion of the USB PHY reset signal. Signed-off-by: Stephan Gerhold <stephan.gerhold@kernkonzept.com> Signed-off-by: Bjorn Andersson <andersson@kernel.org> Link: https://lore.kernel.org/r/20220706134132.3623415-5-stephan.gerhold@kernkonzept.com
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.
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.