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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Date:   Tue, 25 Jul 2023 23:01:19 -0700
From:   Bjorn Andersson <andersson@...nel.org>
To:     Douglas Anderson <dianders@...omium.org>
Cc:     Mark Brown <broonie@...nel.org>,
        Vijaya Krishna Nivarthi <quic_vnivarth@...cinc.com>,
        Andy Gross <agross@...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 Tue, Jul 25, 2023 at 11:02:26AM -0700, 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: Bjorn Andersson <andersson@...nel.org>

Regards,
Bjorn