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If the write protect signal from this IP is connected to the NAND
device, this IP can handle the WP# pin via the WRITE_PROTECT
register.
The Denali NAND Flash Memory Controller User's Guide describes
this register like follows:
When the controller is in reset, the WP# pin is always asserted
to the device. Once the reset is removed, the WP# is de-asserted.
The software will then have to come and program this bit to
assert/de-assert the same.
1 - Write protect de-assert
0 - Write protect assert
The default value is 1, so the write protect is de-asserted after
the reset is removed. The driver can write to the device unless
someone has explicitly cleared register before booting the kernel.
The boot ROM of some UniPhier SoCs (LD4, Pro4, sLD8, Pro5) is the
case; the boot ROM clears the WRITE_PROTECT register when the system
is booting from the NAND device, so the NAND device becomes read-only.
Set it to 1 in the driver in order to allow the write access to the
device.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20200127123934.11847-1-yamada.masahiro@socionext.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.
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.