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: <20200930065513.bwieuiyt4hwwgods@ti.com>
Date:   Wed, 30 Sep 2020 12:25:15 +0530
From:   Pratyush Yadav <p.yadav@...com>
To:     <Tudor.Ambarus@...rochip.com>
CC:     <miquel.raynal@...tlin.com>, <richard@....at>, <vigneshr@...com>,
        <linux-mtd@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
        <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 30/09/20 06:50AM, Tudor.Ambarus@...rochip.com wrote:
> 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?

Yes.
 
> > 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

Ok.

-- 
Regards,
Pratyush Yadav
Texas Instruments India