linux-kernel - Re: [PATCH 4/4] spi: qup: Vote for interconnect bandwidth to DRAM

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Message-ID: <ZQGANOwy97w0RIHV@gerhold.net>
Date:   Wed, 13 Sep 2023 11:26:12 +0200
From:   Stephan Gerhold <stephan@...hold.net>
To:     Stephan Gerhold <stephan.gerhold@...nkonzept.com>
Cc:     Mark Brown <broonie@...nel.org>, Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        linux-arm-msm@...r.kernel.org, linux-spi@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] spi: qup: Vote for interconnect bandwidth to DRAM

On Tue, Sep 12, 2023 at 04:30:39PM +0200, Stephan Gerhold wrote:
> When the SPI QUP controller is used together with a DMA engine it needs
> to vote for the interconnect path to the DRAM. Otherwise it may be
> unable to access the memory quickly enough.

I realized that I argue here that the interconnect vote is for DMA to
DRAM...

> [...]
> @@ -675,6 +698,12 @@ static int spi_qup_io_prep(struct spi_device *spi, struct spi_transfer *xfer)
>  		return -EIO;
>  	}
>  
> +	ret = spi_qup_vote_bw(controller, xfer->speed_hz);
> +	if (ret) {
> +		dev_err(controller->dev, "fail to vote for ICC bandwidth: %d\n", ret);
> +		return -EIO;
> +	}
> +

... but here I vote for the bandwidth even if PIO is used instead of DMA.

I think it would be more logical to only do the bandwidth vote in the
DMA setup path. I'll fix this in v2.

Thanks,
Stephan