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Sometimes, writes fail because the tWB_max is not correctly observed after sending PAGEPROG. It leads to the R/B pin to be read as in the "ready" state right after sending the command, thus preventing the normal tPROG delay to be actually observed. This happens because the ndelay() that waits for tWB_max starts before the command reaches the NAND chip. Add a dummy read when a delay is requested at the end of the executed instruction to make sure that the sent command is received by the NAND before starting the short ndelay() (<1us but rounded up to 1us in practice). This read is done on the control register area because doing it on the Async Data area would change the NAND's RE pin state. This is not perfect as the two areas are behind two different devm_ioremap_resource() and could possibly be located on different interconnects (I did not find more details). This means either the additional latency due to the load operation is enough impacting, or it has the expected behavior of ensuring the write has been received. This has been tested on two platforms designed off of the DAVINCI/OMAP-L138. The first uses a Toshiba NAND Flash (TC58NYG2S3EBAI5), the other a Macronix one (MX30UF4G18AC). Signed-off-by: Bastien Curutchet <bastien.curutchet@bootlin.com> Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com> Link: https://lore.kernel.org/linux-mtd/20240308074609.9056-1-bastien.curutchet@bootlin.com
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 reStructuredText 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.