linux-kernel - Re: [PATCH 1/9] spi: atmel-quadspi: optimize qspi init

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Message-ID: <20190130181505.4f495d3a@bbrezillon>
Date:   Wed, 30 Jan 2019 18:15:15 +0100
From:   Boris Brezillon <bbrezillon@...nel.org>
To:     <Tudor.Ambarus@...rochip.com>
Cc:     <broonie@...nel.org>, <Nicolas.Ferre@...rochip.com>,
        <alexandre.belloni@...tlin.com>, <Ludovic.Desroches@...rochip.com>,
        linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-spi@...r.kernel.org
Subject: Re: [PATCH 1/9] spi: atmel-quadspi: optimize qspi init

On Wed, 30 Jan 2019 15:08:29 +0000
<Tudor.Ambarus@...rochip.com> wrote:

> From: Tudor Ambarus <tudor.ambarus@...rochip.com>
> 
> Set the QSPI controller in Serial Memory Mode at init and not
> at each exec_op() call.

If you ever want to support regular SPI you'll have to put it back to
atmel_qspi_exec_op(), so I'm not sure this is a good move. Another
approach would be to cache the MR value to avoid doing a write access
on the bus when the value hasn't changed.

> 
> Signed-off-by: Tudor Ambarus <tudor.ambarus@...rochip.com>
> ---
>  drivers/spi/atmel-quadspi.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/spi/atmel-quadspi.c b/drivers/spi/atmel-quadspi.c
> index ddc712410812..f79b17792a11 100644
> --- a/drivers/spi/atmel-quadspi.c
> +++ b/drivers/spi/atmel-quadspi.c
> @@ -238,8 +238,6 @@ static int atmel_qspi_exec_op(struct spi_mem *mem, const struct spi_mem_op *op)
>  	icr = QSPI_ICR_INST(op->cmd.opcode);
>  	ifr = QSPI_IFR_INSTEN;
>  
> -	qspi_writel(aq, QSPI_MR, QSPI_MR_SMM);
> -
>  	mode = find_mode(op);
>  	if (mode < 0)
>  		return -ENOTSUPP;
> @@ -381,6 +379,9 @@ static int atmel_qspi_init(struct atmel_qspi *aq)
>  	/* Reset the QSPI controller */
>  	qspi_writel(aq, QSPI_CR, QSPI_CR_SWRST);
>  
> +	/* Set the QSPI controller in Serial Memory Mode */
> +	qspi_writel(aq, QSPI_MR, QSPI_MR_SMM);
> +
>  	/* Enable the QSPI controller */
>  	qspi_writel(aq, QSPI_CR, QSPI_CR_QSPIEN);
>