linux-kernel - Re: [PATCH] mtd: spi-nor: Only set Micron quad-read mode when controller in 4-lane TX mode

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Message-ID: <CAM=Q2cverJLnbUBtyR6S3on79W6cmf8doPAd6T22WwbeqTfkTA@mail.gmail.com>
Date:	Tue, 30 Jun 2015 20:35:15 +0530
From:	Shubhrajyoti Datta <omaplinuxkernel@...il.com>
To:	Mike Looijmans <mike.looijmans@...ic.nl>
Cc:	linux-mtd@...ts.infradead.org, git@...inx.com,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	beanhuo@...ron.com, David Woodhouse <dwmw2@...radead.org>,
	computersforpeace@...il.com
Subject: Re: [PATCH] mtd: spi-nor: Only set Micron quad-read mode when
 controller in 4-lane TX mode

On Tue, Jun 30, 2015 at 4:47 PM, Mike Looijmans <mike.looijmans@...ic.nl> wrote:
> Micron QUAD mode expects command, address and data on 4 lanes instead of just
> one for command (extended SPI mode). This requires the controller to be in a
> special mode, so check first if the controller could be in that mode. If a
> controller does not have the SPI_TX_QUAD mode set, this setting has no chance
> of being valid at all, so don't try to enable it then, and just keep using
> the extended SPI mode.
>
> Tested on a Zynq 7000 with a n25q256a flash chip, this failed to function
> because of the introduction of:
> "driver:mtd:spi-nor: Add quad I/O support for Micron spi nor"
> This commit sets QUAD mode for most Micron chips without asking the controller
> whether it's possible to do so, and without telling the controller that a
> different mode is required, so it couldn't work.
>
> Signed-off-by: Mike Looijmans <mike.looijmans@...ic.nl>
> ---
>  drivers/mtd/spi-nor/spi-nor.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
> index e8f6131..10ba94f 100644
> --- a/drivers/mtd/spi-nor/spi-nor.c
> +++ b/drivers/mtd/spi-nor/spi-nor.c
> @@ -1398,6 +1398,8 @@ static int set_quad_mode(struct spi_nor *nor, struct flash_info *info)
>                 }
>                 return status;
>         case CFI_MFR_ST:
> +               if (!(nor->spi->mode & SPI_TX_QUAD))
> +                       return 0;

Should we return 0 ?

>                 status = micron_quad_enable(nor);
>                 if (status) {
>                         dev_err(nor->dev, "Micron quad-read not enabled\n");
> --
> 1.9.1
>
> --
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