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NAND devices need additional data area (OOB) for error correction, but it is also used for Bad Block Marker (BBM). In many cases, the first byte in OOB is used for BBM, but the location actually depends on chip vendors. The NAND controller should preserve the precious BBM to keep track of bad blocks. In Denali IP, the SPARE_AREA_SKIP_BYTES register is used to specify the number of bytes to skip from the start of OOB. The ECC engine will automatically skip the specified number of bytes when it gets access to OOB area. The same value for SPARE_AREA_SKIP_BYTES should be used between firmware and the operating system if you intend to use the NAND device across the control hand-off. In fact, the current denali.c code expects firmware to have already set the SPARE_AREA_SKIP_BYTES register, then reads the value out. If no firmware (or bootloader) has initialized the controller, the register value is zero, which is the default after power-on-reset. In other words, the Linux driver cannot initialize the controller by itself. Some possible solutions are: [1] Add a DT property to specify the skipped bytes in OOB [2] Associate the preferred value with compatible [3] Hard-code the default value in the driver My first attempt was [1], but in the review process, [3] was suggested as a counter-implementation. (https://lore.kernel.org/patchwork/patch/983055/) The default value 8 was chosen to match to the boot ROM of the UniPhier platform. The preferred value may vary by platform. If so, please trade up to a different solution. Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com> Reviewed-by: Boris Brezillon <boris.brezillon@bootlin.com> Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com> |
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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.
See Documentation/00-INDEX for a list of what is contained in each file.
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.