linux-kernel - Re: [PATCH v2 1/4] spi: cadence-quadspi: Reset CMD

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Message-ID: <mafs07cx8f1oc.fsf_-_@amazon.de>
Date:   Fri, 27 Jan 2023 16:16:19 +0100
From:   Pratyush Yadav <ptyadav@...zon.de>
To:     Dhruva Gole <d-gole@...com>
CC:     Mark Brown <broonie@...nel.org>, <linux-spi@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        Vignesh Raghavendra <vigneshr@...com>,
        Vaishnav Achath <vaishnav.a@...com>,
        <linux-mtd@...ts.infradead.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <Takahiro.Kuwano@...ineon.com>
Subject: Re: [PATCH v2 1/4] spi: cadence-quadspi: Reset CMD_CTRL Reg on cmd
 r/w completion


Hi,

On Wed, Jan 25 2023, Dhruva Gole wrote:

> If one leaves the CQSPI_REG_CMDCTRL in an unclean state this may cause
> issues in future command reads. This issue came to light when some flash
> reads in STIG mode were coming back dirty.

Can you explain in more detail what you mean by "reads coming back
dirty"? Because I don't see any clear reason why not resetting the
register would break anything. We re-create the register value from the
scratch on the next read anyway, and as soon as you writel() that, the
old fields get thrown away anyway.

>
> Signed-off-by: Dhruva Gole <d-gole@...com>
> ---
>  drivers/spi/spi-cadence-quadspi.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/spi/spi-cadence-quadspi.c b/drivers/spi/spi-cadence-quadspi.c
> index 676313e1bdad..6030da942c6e 100644
> --- a/drivers/spi/spi-cadence-quadspi.c
> +++ b/drivers/spi/spi-cadence-quadspi.c
> @@ -549,6 +549,9 @@ static int cqspi_command_read(struct cqspi_flash_pdata *f_pdata,
>                 memcpy(rxbuf, &reg, read_len);
>         }
>
> +       /* Reset CMD_CTRL Reg once command read completes */
> +       writel(0, reg_base + CQSPI_REG_CMDCTRL);
> +
>         return 0;
>  }
>
> @@ -613,7 +616,12 @@ static int cqspi_command_write(struct cqspi_flash_pdata *f_pdata,
>                 }
>         }
>
> -       return cqspi_exec_flash_cmd(cqspi, reg);
> +       ret = cqspi_exec_flash_cmd(cqspi, reg);
> +
> +       /* Reset CMD_CTRL Reg once command write completes */
> +       writel(0, reg_base + CQSPI_REG_CMDCTRL);
> +
> +       return ret;
>  }
>
>  static int cqspi_read_setup(struct cqspi_flash_pdata *f_pdata,
> --
> 2.25.1
>

-- 
Regards,
Pratyush Yadav



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