linux-kernel - Re: [PATCH 1/2] mtd: spi-nor: add an option to force 3byte adressing mode

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Message-ID: <CAMuHMdX0b=J9AuPAvdRXGGVXvc7f9n7TJ0_VKR13P05toq9REw@mail.gmail.com>
Date:   Mon, 28 Aug 2017 23:18:25 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Marcin Wojtas <mw@...ihalf.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        MTD Maling List <linux-mtd@...ts.infradead.org>,
        linux-spi <linux-spi@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Will Deacon <will.deacon@....com>,
        Cyrille Pitchen <cyrille.pitchen@...ev4u.fr>,
        Marek Vasut <marek.vasut@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
        Gregory Clement <gregory.clement@...e-electrons.com>,
        Nadav Haklai <nadavh@...vell.com>, neta@...vell.com,
        omrii@...vell.com, Hanna Hawa <hannah@...vell.com>,
        Grzegorz Jaszczyk <jaz@...ihalf.com>, tn@...ihalf.com
Subject: Re: [PATCH 1/2] mtd: spi-nor: add an option to force 3byte adressing mode

On Mon, Aug 28, 2017 at 11:14 PM, Marcin Wojtas <mw@...ihalf.com> wrote:
> Hitherto code set 4B addressing mode for all SPI flashes whose
> size exceeds 16MB. However, changing the default 3B access
> in some cases may be harmful - it may happen that the Boot ROM
> is not capable of handling non-default state of the SPI NOR
> (e.g. after soft reset). Some flash devices allow to access the
> memory above 128Mib without changing mode to 4byte thanks
> to special op codes (see SPI_NOR_4B_OPCODES flag). Unfortunately
> for those which don't support them, the problem persists.
>
> This patch adds optional property that can be added to the
> SPI flash node and which will force to use 3B addressing mode,
> limiting the accessible memory size to 16MiB.
> Binding documentation is updated accordingly.
>
> Signed-off-by: Marcin Wojtas <mw@...ihalf.com>
> ---
>  Documentation/devicetree/bindings/spi/spi-bus.txt |  2 ++
>  drivers/mtd/spi-nor/spi-nor.c                     | 12 +++++++++++-
>  2 files changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/devicetree/bindings/spi/spi-bus.txt b/Documentation/devicetree/bindings/spi/spi-bus.txt
> index 1f6e86f..f13b773 100644
> --- a/Documentation/devicetree/bindings/spi/spi-bus.txt
> +++ b/Documentation/devicetree/bindings/spi/spi-bus.txt
> @@ -77,6 +77,8 @@ All slave nodes can contain the following optional properties:
>                     Defaults to 1 if not present.
>  - spi-rx-delay-us - Microsecond delay after a read transfer.
>  - spi-tx-delay-us - Microsecond delay after a write transfer.
> +- spi-3byte-addressing - Empty property indicating device access to be done
> +                   only in 3byte addressing mode.

spi-force-3byte-addressing?

>  Some SPI controllers and devices support Dual and Quad SPI transfer mode.
>  It allows data in the SPI system to be transferred using 2 wires (DUAL) or 4
> diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
> index 1413828..029c87d 100644
> --- a/drivers/mtd/spi-nor/spi-nor.c
> +++ b/drivers/mtd/spi-nor/spi-nor.c
> @@ -2002,7 +2002,17 @@ int spi_nor_scan(struct spi_nor *nor, const char *name,
>                 if (JEDEC_MFR(info) == SNOR_MFR_SPANSION ||
>                     info->flags & SPI_NOR_4B_OPCODES)
>                         spi_nor_set_4byte_opcodes(nor, info);
> -               else
> +               else if (of_property_read_bool(np, "spi-3byte-addressing")) {
> +                       /*
> +                        * Do not enter 4byte mode in order to prevent
> +                        * the early bootloader to come up on non-default
> +                        * SPI NOR memory during boot. Limit accessible
> +                        * size to 16MiB.
> +                        */
> +                       nor->addr_width = 3;
> +                       mtd->size = 0x1000000;

What if the device is smaller than 16 MiB?

mtd->size = min(mtd->size, 0x1000000);

> +                       dev_info(dev, "Force 3B addressing mode\n");
> +               } else
>                         set_4byte(nor, info, 1);
>         } else {
>                 nor->addr_width = 3;

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds