linux-kernel - Re: [PATCH 2/2] spi: spi-qcom-qspi: Add mem_ops to avoid PIO for badly sized reads

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Message-ID: <faa31984-7185-6d25-dbb7-3e25e0883e5b@quicinc.com>
Date:   Wed, 26 Jul 2023 12:57:48 +0530
From:   Vijaya Krishna Nivarthi <quic_vnivarth@...cinc.com>
To:     Douglas Anderson <dianders@...omium.org>,
        Mark Brown <broonie@...nel.org>
CC:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        <linux-arm-msm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-spi@...r.kernel.org>
Subject: Re: [PATCH 2/2] spi: spi-qcom-qspi: Add mem_ops to avoid PIO for
 badly sized reads


On 7/25/2023 11:32 PM, Douglas Anderson wrote:
> In the patch ("spi: spi-qcom-qspi: Fallback to PIO for xfers that
> aren't multiples of 4 bytes") we detect reads that we can't handle
> properly and fallback to PIO mode. While that's correct behavior, we
> can do better by adding "spi_controller_mem_ops" for our
> controller. Once we do this then the caller will give us a transfer
> that's a multiple of 4-bytes so we can DMA.
>
> Fixes: b5762d95607e ("spi: spi-qcom-qspi: Add DMA mode support")
> Signed-off-by: Douglas Anderson <dianders@...omium.org>

I checked with a couple of folks here and seemingly the POR for QSPI 
controller is for storage device only, so in all likelihood we should be 
having a spi-flash at the other end.

For other devices there is QUP anyway.

Hence personally I am happy with this change.

Thank you...


Reviewed-by: Vijaya Krishna Nivarthi <quic_vnivarth@...cinc.com>


> ---
>
>   drivers/spi/spi-qcom-qspi.c | 25 +++++++++++++++++++++++++
>   1 file changed, 25 insertions(+)
>
> diff --git a/drivers/spi/spi-qcom-qspi.c b/drivers/spi/spi-qcom-qspi.c
> index 39b4d8a8107a..b2bbcfd93637 100644
> --- a/drivers/spi/spi-qcom-qspi.c
> +++ b/drivers/spi/spi-qcom-qspi.c
> @@ -659,6 +659,30 @@ static irqreturn_t qcom_qspi_irq(int irq, void *dev_id)
>   	return ret;
>   }
>   
> +static int qcom_qspi_adjust_op_size(struct spi_mem *mem, struct spi_mem_op *op)
> +{
> +	/*
> +	 * If qcom_qspi_can_dma() is going to return false we don't need to
> +	 * adjust anything.
> +	 */
> +	if (op->data.nbytes <= QSPI_MAX_BYTES_FIFO)
> +		return 0;
> +
> +	/*
> +	 * When reading, the transfer needs to be a multiple of 4 bytes so
> +	 * shrink the transfer if that's not true. The caller will then do a
> +	 * second transfer to finish things up.
> +	 */
> +	if (op->data.dir == SPI_MEM_DATA_IN && (op->data.nbytes & 0x3))
> +		op->data.nbytes &= ~0x3;
> +
> +	return 0;
> +}
> +
> +static const struct spi_controller_mem_ops qcom_qspi_mem_ops = {
> +	.adjust_op_size = qcom_qspi_adjust_op_size,
> +};
> +
>   static int qcom_qspi_probe(struct platform_device *pdev)
>   {
>   	int ret;
> @@ -743,6 +767,7 @@ static int qcom_qspi_probe(struct platform_device *pdev)
>   	if (of_property_read_bool(pdev->dev.of_node, "iommus"))
>   		master->can_dma = qcom_qspi_can_dma;
>   	master->auto_runtime_pm = true;
> +	master->mem_ops = &qcom_qspi_mem_ops;
>   
>   	ret = devm_pm_opp_set_clkname(&pdev->dev, "core");
>   	if (ret)