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SubjectRe: [PATCH 1/2] spi: spi-qcom-qspi: Fallback to PIO for xfers that aren't multiples of 4 bytes
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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@chromium.org>

Reviewed-by: Vijaya Krishna Nivarthi <quic_vnivarth@quicinc.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++) {

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