linux-kernel - Re: [PATCH v13 08/15] mtd: spi-nor: core: do 2 byte reads for SR and FSR in DTR mode

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Message-ID: <6198a69a-2800-d14f-1d29-9511ba6a3f5f@microchip.com>
Date:   Wed, 30 Sep 2020 06:50:09 +0000
From:   <Tudor.Ambarus@...rochip.com>
To:     <p.yadav@...com>, <miquel.raynal@...tlin.com>, <richard@....at>,
        <vigneshr@...com>, <linux-mtd@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
CC:     <nsekhar@...com>, <boris.brezillon@...labora.com>
Subject: Re: [PATCH v13 08/15] mtd: spi-nor: core: do 2 byte reads for SR and
 FSR in DTR mode

On 9/16/20 3:44 PM, Pratyush Yadav wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> Some controllers, like the cadence qspi controller, have trouble reading
> only 1 byte in DTR mode. So, do 2 byte reads for SR and FSR commands in

did you get garbage when reading only one byte?

> DTR mode, and then discard the second byte.
> 
> Signed-off-by: Pratyush Yadav <p.yadav@...com>
> ---
>  drivers/mtd/spi-nor/core.c | 15 +++++++++++++--
>  1 file changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/mtd/spi-nor/core.c b/drivers/mtd/spi-nor/core.c
> index 88c9e18067f4..87c568debf14 100644
> --- a/drivers/mtd/spi-nor/core.c
> +++ b/drivers/mtd/spi-nor/core.c
> @@ -368,7 +368,7 @@ int spi_nor_write_disable(struct spi_nor *nor)
>   * spi_nor_read_sr() - Read the Status Register.
>   * @nor:       pointer to 'struct spi_nor'.
>   * @sr:                pointer to a DMA-able buffer where the value of the
> - *              Status Register will be written.
> + *              Status Register will be written. Should be at least 2 bytes.
>   *
>   * Return: 0 on success, -errno otherwise.
>   */
> @@ -386,6 +386,11 @@ static int spi_nor_read_sr(struct spi_nor *nor, u8 *sr)
>                 if (spi_nor_protocol_is_dtr(nor->reg_proto)) {
>                         op.addr.nbytes = nor->params->rdsr_addr_nbytes;
>                         op.dummy.nbytes = nor->params->rdsr_dummy;
> +                       /*
> +                        * We don't want to read only one byte in DTR mode. So,
> +                        * read 2 and then discard the second byte.
> +                        */
> +                       op.data.nbytes = 2;

just for octal dtr, but should be fine if you update the previous patch

>                 }
> 
>                 spi_nor_spimem_setup_op(nor, &op, nor->reg_proto);
> @@ -405,7 +410,8 @@ static int spi_nor_read_sr(struct spi_nor *nor, u8 *sr)
>   * spi_nor_read_fsr() - Read the Flag Status Register.
>   * @nor:       pointer to 'struct spi_nor'
>   * @fsr:       pointer to a DMA-able buffer where the value of the
> - *              Flag Status Register will be written.
> + *              Flag Status Register will be written. Should be at least 2
> + *              bytes.
>   *
>   * Return: 0 on success, -errno otherwise.
>   */
> @@ -423,6 +429,11 @@ static int spi_nor_read_fsr(struct spi_nor *nor, u8 *fsr)
>                 if (spi_nor_protocol_is_dtr(nor->reg_proto)) {
>                         op.addr.nbytes = nor->params->rdsr_addr_nbytes;
>                         op.dummy.nbytes = nor->params->rdsr_dummy;
> +                       /*
> +                        * We don't want to read only one byte in DTR mode. So,
> +                        * read 2 and then discard the second byte.
> +                        */
> +                       op.data.nbytes = 2;
>                 }
> 
>                 spi_nor_spimem_setup_op(nor, &op, nor->reg_proto);
> --
> 2.28.0
>