spi: spi-qcom-qspi: Fallback to PIO for xfers that aren't multiples of 4 bytes

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>
Reviewed-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20230725110226.1.Ia2f980fc7cd0b831e633391f0bb1272914d8f381@changeid
Signed-off-by: Mark Brown <broonie@kernel.org>

diff --git a/drivers/spi/spi-qcom-qspi.c b/drivers/spi/spi-qcom-qspi.c
index 9b3092e..db1dd13 100644 (file)
--- a/drivers/spi/spi-qcom-qspi.c
+++ b/drivers/spi/spi-qcom-qspi.c
@@ -357,10 +357,22 @@ 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++) {