linux-kernel - Re: [PATCH 1/3] mtd: spi-nor: Add Octal mode support for mt35xu512aba

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Date:   Thu, 4 Oct 2018 11:45:35 +0200
From:   Boris Brezillon <boris.brezillon@...tlin.com>
To:     Vignesh R <vigneshr@...com>
Cc:     Marek Vasut <marek.vasut@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Brian Norris <computersforpeace@...il.com>,
        Yogesh Gaur <yogeshnarayan.gaur@....com>,
        Linux ARM Mailing List <linux-arm-kernel@...ts.infradead.org>,
        <linux-mtd@...ts.infradead.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] mtd: spi-nor: Add Octal mode support for
 mt35xu512aba

On Wed, 3 Oct 2018 22:26:01 +0530
Vignesh R <vigneshr@...com> wrote:

> Micron's mt35xu512aba flash is an Octal flash that has x8 IO lines. It
> supports read/write over 8 IO lines simulatenously. Add support for
> Octal read mode for Micron mt35xu512aba.
> Unfortunately, this flash is only complaint to SFDP JESD216B and does not
> seem to support newer JESD216C standard that provides auto detection of
> Octal mode capabilities and opcodes. Therefore, this capability is
> manually added using new SPI_NOR_OCTAL_READ flag.
> 
> Signed-off-by: Vignesh R <vigneshr@...com>
> ---
>  drivers/mtd/spi-nor/spi-nor.c | 11 ++++++++++-
>  include/linux/mtd/spi-nor.h   |  2 ++
>  2 files changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
> index aff5e6ff0b2c..4926e805a8cb 100644
> --- a/drivers/mtd/spi-nor/spi-nor.c
> +++ b/drivers/mtd/spi-nor/spi-nor.c
> @@ -90,6 +90,7 @@ struct flash_info {
>  #define NO_CHIP_ERASE		BIT(12) /* Chip does not support chip erase */
>  #define SPI_NOR_SKIP_SFDP	BIT(13)	/* Skip parsing of SFDP tables */
>  #define USE_CLSR		BIT(14)	/* use CLSR command */
> +#define SPI_NOR_OCTAL_READ	BIT(15)	/* Flash supports Octal Read */

Hm, we'll need to clarify what OCTAL means. I see at least 3 different
modes using 8 IO lines (1-1-8, 1-8-8 and 8-8-8) and all of them could
be qualified as "octal" modes.
So how about renaming this macro SPI_NOR_1_1_8_READ.

Also, I fear we'll soon run out of bits in ->flags if we keep adding
one flag per mode which is why I proposed a solution to let flash
chips tweak the flash parameters as they wish [1][2]. I'm not saying we
should do it now, but we should definitely plan for something like that.

[1]https://github.com/bbrezillon/linux/commit/9c672e4c85a91f1b0803c9c6e4b8f3aae5d79ffb
[2]https://github.com/bbrezillon/linux/commit/3a5515c8821314c06a3d84f9861aefe476bb711e