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: <1e7225c2-3ac6-43d0-a1cc-e9a207d263d4@sirena.org.uk>
Date:   Tue, 25 Jul 2023 19:24:07 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Douglas Anderson <dianders@...omium.org>
Cc:     Vijaya Krishna Nivarthi <quic_vnivarth@...cinc.com>,
        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 Tue, Jul 25, 2023 at 11:02:27AM -0700, 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.

This is more of an optimisation for the case where we're using flash -
if someone has hung some other hardware off the controller (which seems
reasonable enough if they don't need it for flash) then we'll not use
the mem_ops.

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