• Stephen Boyd's avatar
    usb: ulpi: Support device discovery via DT · ef6a7bcf
    Stephen Boyd authored
    The qcom HSIC ULPI phy doesn't have any bits set in the vendor or
    product ID registers. This makes it impossible to make a ULPI
    driver match against the ID registers. Add support to discover
    the ULPI phys via DT help alleviate this problem. In the DT case,
    we'll look for a ULPI bus node underneath the device registering
    the ULPI viewport (or the parent of that device to support
    chipidea's device layout) and then match up the phy node
    underneath that with the ULPI device that's created.
    
    The side benefit of this is that we can use standard properties
    in the phy node like clks, regulators, gpios, etc. because we
    don't have firmware like ACPI to turn these things on for us. And
    we can use the DT phy binding to point our phy consumer to the
    phy provider.
    
    The ULPI bus code supports native enumeration by reading the
    vendor ID and product ID registers at device creation time, but
    we can't be certain that those register reads will succeed if the
    phy is not powered up. To avoid any problems with reading the ID
    registers before the phy is powered we fallback to DT matching
    when the ID reads fail.
    
    If the ULPI spec had some generic power sequencing for these
    registers we could put that into the ULPI bus layer and power up
    the device before reading the ID registers. Unfortunately this
    doesn't exist and the power sequence is usually device specific.
    By having the device matched up with DT we can avoid this
    problem.
    
    Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    Acked-by: default avatarHeikki Krogerus <heikki.krogerus@linux.intel.com>
    Cc: <devicetree@vger.kernel.org>
    Acked-by: default avatarRob Herring <robh@kernel.org>
    Signed-off-by: default avatarStephen Boyd <stephen.boyd@linaro.org>
    Signed-off-by: default avatarPeter Chen <peter.chen@nxp.com>
    ef6a7bcf
ulpi.txt 401 Bytes