linux-kernel - Re: [PATCH 7/7] arm64: dts: qcom: sdm845: enable dma for spi

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Date:   Tue, 12 Jan 2021 09:49:44 +0530
From:   Vinod Koul <vkoul@...nel.org>
To:     Konrad Dybcio <konrad.dybcio@...ainline.org>
Cc:     Bjorn Andersson <bjorn.andersson@...aro.org>,
        Mark Brown <broonie@...nel.org>, Wolfram Sang <wsa@...nel.org>,
        linux-arm-msm@...r.kernel.org, Andy Gross <agross@...nel.org>,
        Matthias Kaehlcke <mka@...omium.org>,
        Douglas Anderson <dianders@...omium.org>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Amit Pundir <amit.pundir@...aro.org>,
        linux-spi@...r.kernel.org, linux-i2c@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 7/7] arm64: dts: qcom: sdm845: enable dma for spi

On 11-01-21, 21:45, Konrad Dybcio wrote:
> 
> > If it is working without GPI enabled, it would work.. GPI for QUP is
> > something that requires firmware and would have to be enabled by
> > firmware
> 
> 
> I think with the new code of yours:
> 
> 
> mas->tx = dma_request_slave_channel(mas->dev, "tx");
> + if (IS_ERR_OR_NULL(mas->tx)) {
> + dev_err(mas->dev, "Failed to get tx DMA ch %ld", PTR_ERR(mas->tx)); ret = PTR_ERR(mas->tx); + goto out_pm;

This code would be exercised *only* when DMA mode is enabled in
firmware.. Both SPI and I2C driver would probe the mode supported
(reason for exposing stuff in first two patches of this series)..

Only if the device reports we should enable it.. Also if the device is
working with FIFO mode then DMA mode wont work..

> 
> it *may* fail to probe with the channels assigned in the "dmas="
> property but with the engine having "status=disabled", but as I don't
> have any hardware to test that driver on, please confirm whether my
> concerns are right..
> 
> 
> > Since DMA support may not be available on certain targets (firmware
> > support), so enabling per board would make sense
> 
> Oh really, are there SDM845 boards shipping with GPI DMA *disabled to
> all peripherals*?

Is the peripheral working with FIFO mode, then answer is yes :)

Thanks
-- 
~Vinod