linux-kernel - Re: [PATCH v3 01/13] spi: atmel-quadspi: cache MR value to avoid a write access

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Date:   Sat, 2 Feb 2019 08:06:50 +0100
From:   Boris Brezillon <bbrezillon@...nel.org>
To:     <Tudor.Ambarus@...rochip.com>
Cc:     <broonie@...nel.org>, <robh+dt@...nel.org>, <mark.rutland@....com>,
        <Nicolas.Ferre@...rochip.com>, <alexandre.belloni@...tlin.com>,
        <Ludovic.Desroches@...rochip.com>, <Cyrille.Pitchen@...rochip.com>,
        <bugalski.piotr@...il.com>, <linux-spi@...r.kernel.org>,
        <devicetree@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <linux-mtd@...ts.infradead.org>
Subject: Re: [PATCH v3 01/13] spi: atmel-quadspi: cache MR value to avoid a
 write access

On Sat, 2 Feb 2019 04:07:13 +0000
<Tudor.Ambarus@...rochip.com> wrote:

> From: Tudor Ambarus <tudor.ambarus@...rochip.com>
> 
> Cache Serial Memory Mode (SMM) value to avoid write access when
> setting the controller in serial memory mode. SMM is set in
> exec_op() and not at probe time, to let room for future regular
> SPI support.
> 
> Signed-off-by: Tudor Ambarus <tudor.ambarus@...rochip.com>
> ---
> v3: update smm value when different. rename mr/smm
> v2: cache MR value instead of moving the write access at probe
> 
>  drivers/spi/atmel-quadspi.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/spi/atmel-quadspi.c b/drivers/spi/atmel-quadspi.c
> index ddc712410812..645284c6ec9a 100644
> --- a/drivers/spi/atmel-quadspi.c
> +++ b/drivers/spi/atmel-quadspi.c
> @@ -155,6 +155,7 @@ struct atmel_qspi {
>  	struct clk		*clk;
>  	struct platform_device	*pdev;
>  	u32			pending;
> +	u32			smm;
>  	struct completion	cmd_completion;
>  };
>  
> @@ -238,7 +239,11 @@ 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);
> +	/* Set the QSPI controller in Serial Memory Mode */
> +	if (aq->smm != QSPI_MR_SMM) {

Sorry, I think I misunderstood your previous suggestion, I thought the
reg was called SMM. If the reg is called MR and the value you expect in
there is SMM, then the field should be named ->mr as it caches the
whole reg, not only the SMM bit. So it's actually:

	if (aq->mr != QSPI_MR_SMM) {

> +		qspi_writel(aq, QSPI_MR, QSPI_MR_SMM);
> +		aq->smm = QSPI_MR_SMM;
> +	}
>  
>  	mode = find_mode(op);
>  	if (mode < 0)