linux-kernel - Re: [PATCH] mtd: rawnand: denali: add reset controlling

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Date:   Thu, 19 Dec 2019 14:07:26 -0600
From:   Rob Herring <robh@...nel.org>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     linux-mtd@...ts.infradead.org, Dinh Nguyen <dinguyen@...nel.org>,
        Marek Vasut <marex@...x.de>,
        Ley Foon Tan <ley.foon.tan@...el.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Mark Rutland <mark.rutland@....com>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mtd: rawnand: denali: add reset controlling

On Tue, 10 Dec 2019 18:14:53 +0900, Masahiro Yamada wrote:
> According to the Denali User's Guide, this IP has two reset signals.
> 
>   rst_n:     reset most of FFs in the controller core
>   reg_rst_n: reset all FFs in the register interface, and in the
>              initialization sequence
> 
> This commit supports controlling those reset signals, although they
> might be often tied up together in actual SoC integration.
> 
> One thing that should be kept in mind is the automated initialization
> sequence (a.k.a. 'bootstrap' process) is kicked off when reg_rst_n is
> deasserted.
> 
> When the reset is deasserted, the controller issues a RESET command
> to the chip select 0, and attempts to read out the chip ID, and further
> more, ONFI parameters if it is an ONFI-compliant device. Then, the
> controller sets up the relevant registers based on the detected
> device parameters.
> 
> This process is just redundant for Linux because nand_scan_ident()
> probes devices and sets up parameters accordingly. Rather, this hardware
> feature is annoying because it ends up with misdetection due to bugs.
> 
> So, commit 0615e7ad5d52 ("mtd: nand: denali: remove Toshiba and Hynix
> specific fixup code") changed the driver to not rely on it.
> 
> However, there is no way to prevent it from running. The IP provides
> the 'bootstrap_inhibit_init' port to suppress this sequence, but it is
> usually out of software control, and dependent on SoC implementation.
> As for the Socionext UniPhier platform, LD4 always enables it. For the
> later SoCs, the bootstrap sequence runs depending on the boot mode.
> 
> I added usleep_range() to make the driver wait until the sequence
> finishes. Otherwise, the driver would fail to detect the chip due
> to the race between the driver and hardware-controlled sequence.
> 
> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
> ---
> 
>  .../devicetree/bindings/mtd/denali-nand.txt   |  7 ++++
>  drivers/mtd/nand/raw/denali_dt.c              | 40 ++++++++++++++++++-
>  2 files changed, 46 insertions(+), 1 deletion(-)
> 

Acked-by: Rob Herring <robh@...nel.org>