linux-kernel - Re: [PATCH] mtd: rawnand: denali: deassert write protect pin

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Date:   Tue, 10 Mar 2020 19:33:51 +0100
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>,
        linux-mtd@...ts.infradead.org
Cc:     Miquel Raynal <miquel.raynal@...tlin.com>,
        Vignesh Raghavendra <vigneshr@...com>,
        Boris Brezillon <bbrezillon@...nel.org>,
        Richard Weinberger <richard@....at>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mtd: rawnand: denali: deassert write protect pin

On Mon, 2020-01-27 at 12:39:34 UTC, Masahiro Yamada wrote:
> 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@...ionext.com>

Applied to https://git.kernel.org/pub/scm/linux/kernel/git/mtd/linux.git nand/next, thanks.

Miquel