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Marek Vasut a4b2e6063c firmware: xilinx: Clear IOCTL_SET_SD_TAPDELAY using PM_MMIO_WRITE
In case the tap delay required by Arasan SDHCI is set to 0, the current
embeddedsw firmware unconditionally writes IOU_SLCR SD_ITAPDLY to 0x100
(SD0_ITAPDLYENA=1, SD0_ITAPDLYSEL=0). Previous behavior was to keep the
IOU_SLCR SD_ITAPDLY set to 0x0. There is some sort of difference in the
behavior between SD0_ITAPDLYENA=1/0 with the same SD0_ITAPDLYSEL=0, even
though the behavior should be identical -- zero delay added to rxclk_in
line. The former breaks HS200 training in low temperature conditions.

Write IOU_SLCR SD_ITAPDLY register to 0 using PM_MMIO_WRITE which seem
to allow unrestricted WRITE access (and PM_MMIO_READ which allows read
access) to the entire address space. This way, it is possible to work
around the defect in IOCTL_SET_SD_TAPDELAY design which does not permit
clearing SDx_ITAPDLYENA bit.

Note that the embeddedsw firmware does not permit clearing the SD_ITAPDLY
SD0_ITAPDLYENA bit, this bit can only ever be set by the firmware and it
is often impossible to update the possibly broken firmware.

Signed-off-by: Marek Vasut <marex@denx.de>
Link: https://lore.kernel.org/r/20221215152023.8387-1-marex@denx.de
Signed-off-by: Michal Simek <michal.simek@amd.com>
History 2023-01-05 10:18:07 +01:00
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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.