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[ Upstream commit7a94b83a7d] On SAMA7G5, when resuming from backup and self-refresh, the bootloader performs DDR PHY recalibration by restoring the value of ZQ0SR0 (stored in RAM by Linux before going to backup and self-refresh). It has been discovered that the current procedure doesn't work for all possible values that might go to ZQ0SR0 due to hardware bug. The workaround to this is to avoid storing some values in ZQ0SR0. Thus Linux will read the ZQ0SR0 register and cache its value in RAM after processing it (using modified_gray_code array). The bootloader will restore the processed value. Fixes:d2d4716d83("ARM: at91: pm: save ddr phy calibration data to securam") Suggested-by: Frederic Schumacher <frederic.schumacher@microchip.com> Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com> Link: https://lore.kernel.org/r/20220826083927.3107272-4-claudiu.beznea@microchip.com Signed-off-by: Sasha Levin <sashal@kernel.org>
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.