linux-kernel - Re: [PATCH v2 2/6] mtd: spi-nor: spansion: write 2 bytes when disabling Octal DTR mode

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Date:   Thu, 23 Dec 2021 13:06:14 +0000
From:   <Tudor.Ambarus@...rochip.com>
To:     <p.yadav@...com>, <michael@...le.cc>, <miquel.raynal@...tlin.com>,
        <richard@....at>, <vigneshr@...com>, <broonie@...nel.org>,
        <linux-mtd@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
        <linux-spi@...r.kernel.org>
Subject: Re: [PATCH v2 2/6] mtd: spi-nor: spansion: write 2 bytes when
 disabling Octal DTR mode

On 5/31/21 9:17 PM, Pratyush Yadav wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> The Octal DTR configuration is stored in the CFR5V register. This
> register is 1 byte wide. But 1 byte long transactions are not allowed in
> 8D-8D-8D mode. Since the next byte address does not contain any
> register, it is safe to write any value to it. Write a 0 to it.
> 
> Signed-off-by: Pratyush Yadav <p.yadav@...com>
> ---
> 
> (no changes since v1)
> 
>  drivers/mtd/spi-nor/spansion.c | 18 +++++++++++++-----
>  1 file changed, 13 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/mtd/spi-nor/spansion.c b/drivers/mtd/spi-nor/spansion.c
> index ee82dcd75310..e6bf5c9eee6a 100644
> --- a/drivers/mtd/spi-nor/spansion.c
> +++ b/drivers/mtd/spi-nor/spansion.c
> @@ -65,10 +65,18 @@ static int spi_nor_cypress_octal_dtr_enable(struct spi_nor *nor, bool enable)
>         if (ret)
>                 return ret;
> 
> -       if (enable)
> -               *buf = SPINOR_REG_CYPRESS_CFR5V_OCT_DTR_EN;
> -       else
> -               *buf = SPINOR_REG_CYPRESS_CFR5V_OCT_DTR_DS;
> +       if (enable) {
> +               buf[0] = SPINOR_REG_CYPRESS_CFR5V_OCT_DTR_EN;
> +       } else {
> +               /*
> +                * The register is 1-byte wide, but 1-byte transactions are not
> +                * allowed in 8D-8D-8D mode. Since there is no register at the
> +                * next location, just initialize the value to 0 and let the
> +                * transaction go on.
> +                */
> +               buf[0] = SPINOR_REG_CYPRESS_CFR5V_OCT_DTR_DS;
> +               buf[1] = 0;

how about writing 0xff instead?

> +       }
> 
>         op = (struct spi_mem_op)
>                 SPI_MEM_OP(SPI_MEM_OP_CMD(SPINOR_OP_WR_ANY_REG, 1),
> @@ -76,7 +84,7 @@ static int spi_nor_cypress_octal_dtr_enable(struct spi_nor *nor, bool enable)
>                                            SPINOR_REG_CYPRESS_CFR5V,
>                                            1),
>                            SPI_MEM_OP_NO_DUMMY,
> -                          SPI_MEM_OP_DATA_OUT(1, buf, 1));
> +                          SPI_MEM_OP_DATA_OUT(enable ? 1 : 2, buf, 1));
> 
>         if (!enable)
>                 spi_nor_spimem_setup_op(nor, &op, SNOR_PROTO_8_8_8_DTR);
> --
> 2.30.0
>