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The driver dwc3 deviates from the programming guide in regard to endpoint configuration. It does this command sequence: DEPSTARTCFG -> DEPXFERCFG -> DEPCFG Instead of the suggested flow: DEPSTARTCFG -> DEPCFG -> DEPXFERCFG The reasons for this deviation were as follow, quoted: 1) The databook says to do %DWC3_DEPCMD_DEPSTARTCFG for every %USB_REQ_SET_CONFIGURATION and %USB_REQ_SET_INTERFACE (8.1.5). This is incorrect in the scenario of multiple interfaces. 2) The databook does not mention doing more %DWC3_DEPCMD_DEPXFERCFG for new endpoint on alt setting (8.1.6). Regarding 1), DEPSTARTCFG resets the endpoints' resource and can be a problem if used with SET_INTERFACE request of a multiple interface configuration. But we can still satisfy the programming guide requirement by assigning the endpoint resource as part of usb_ep_enable(). We will only reset endpoint resources on controller initialization and SET_CONFIGURATION request. Regarding 2), the later versions of the programming guide were updated to clarify this flow (see "Alternate Initialization on SetInterface Request" of the programming guide). As long as the platform has enough physical endpoints, we can assign resource to a new endpoint. The order of the command sequence will not be a problem to most platforms for the current implementation of the dwc3 driver. However, this order is required in different scenarios (such as initialization during controller's hibernation restore). Let's keep the flow consistent and follow the programming guide. Signed-off-by: Thinh Nguyen <Thinh.Nguyen@synopsys.com> Link: https://lore.kernel.org/r/c143583a5afb087deb8c3aa5eb227ee23515f272.1706754219.git.Thinh.Nguyen@synopsys.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
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| README | ||
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.