linux-kernel - Re: [PATCH 1/2] spi: spi-qcom-qspi: Fallback to PIO for xfers that aren't multiples of 4 bytes

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Message-ID: <d2cc7c22-6afb-f59e-ae37-0604e362222e@quicinc.com>
Date:   Wed, 26 Jul 2023 11:36:23 +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 1/2] spi: spi-qcom-qspi: Fallback to PIO for xfers that
 aren't multiples of 4 bytes


On 7/25/2023 11:32 PM, Douglas Anderson wrote:
> The Qualcomm QSPI driver appears to require that any reads using DMA
> are a mutliple of 4 bytes. If this isn't true then the controller will
> clobber any extra bytes in memory following the last word. Let's
> detect this and falback to PIO.
>
> This fixes problems reported by slub_debug=FZPUA, which would complain
> about "kmalloc Redzone overwritten". One such instance said:
>
>    0xffffff80c29d541a-0xffffff80c29d541b @offset=21530. First byte 0x0 instead of 0xcc
>    Allocated in mtd_kmalloc_up_to+0x98/0xac age=36 cpu=3 pid=6658
>
> Tracing through what was happening I saw that, while we often did DMA
> tranfers of 0x1000 bytes, sometimes we'd end up doing ones of 0x41a
> bytes. Those 0x41a byte transfers were the problem.
>
> NOTE: a future change will enable the SPI "mem ops" to help avoid this
> case, but it still seems good to add the extra check in the transfer.
>
> Fixes: b5762d95607e ("spi: spi-qcom-qspi: Add DMA mode support")
> Signed-off-by: Douglas Anderson <dianders@...omium.org>

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


Thank you for the fix,

Vijay/


> ---
>
>   drivers/spi/spi-qcom-qspi.c | 12 ++++++++++++
>   1 file changed, 12 insertions(+)
>
> diff --git a/drivers/spi/spi-qcom-qspi.c b/drivers/spi/spi-qcom-qspi.c
> index a0ad9802b606..39b4d8a8107a 100644
> --- a/drivers/spi/spi-qcom-qspi.c
> +++ b/drivers/spi/spi-qcom-qspi.c
> @@ -355,10 +355,22 @@ static int qcom_qspi_setup_dma_desc(struct qcom_qspi *ctrl,
>   
>   	for (i = 0; i < sgt->nents; i++) {
>   		dma_ptr_sg = sg_dma_address(sgt->sgl + i);
> +		dma_len_sg = sg_dma_len(sgt->sgl + i);
>   		if (!IS_ALIGNED(dma_ptr_sg, QSPI_ALIGN_REQ)) {
>   			dev_warn_once(ctrl->dev, "dma_address not aligned to %d\n", QSPI_ALIGN_REQ);
>   			return -EAGAIN;
>   		}
> +		/*
> +		 * When reading with DMA the controller writes to memory 1 word
> +		 * at a time. If the length isn't a multiple of 4 bytes then
> +		 * the controller can clobber the things later in memory.
> +		 * Fallback to PIO to be safe.
> +		 */
> +		if (ctrl->xfer.dir == QSPI_READ && (dma_len_sg & 0x03)) {
> +			dev_warn_once(ctrl->dev, "fallback to PIO for read of size %#010x\n",
> +				      dma_len_sg);
> +			return -EAGAIN;
> +		}
>   	}
>   
>   	for (i = 0; i < sgt->nents; i++) {