linux-kernel - Re: [PATCH 2/3] arm64: dts: qcom: sm8350: Add GENI I2C/SPI DMA channels

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Message-ID: <Yl0Q/Hbkyp5/sH8T@matsya>
Date:   Mon, 18 Apr 2022 12:49:24 +0530
From:   Vinod Koul <vkoul@...nel.org>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] arm64: dts: qcom: sm8350: Add GENI I2C/SPI DMA
 channels

On 12-04-22, 20:57, Bjorn Andersson wrote:
> On Tue 12 Apr 20:14 PDT 2022, Vinod Koul wrote:
> 
> > On 12-04-22, 14:51, Bjorn Andersson wrote:
> > > The GENI I2C and SPI controllers may use the GPI DMA engine, define the
> > > rx and tx channels for these controllers to enable this.
> > > 
> > > Signed-off-by: Bjorn Andersson <bjorn.andersson@...aro.org>
> > > ---
> > >  arch/arm64/boot/dts/qcom/sm8350.dtsi | 108 +++++++++++++++++++++++++++
> > >  1 file changed, 108 insertions(+)
> > > 
> > > diff --git a/arch/arm64/boot/dts/qcom/sm8350.dtsi b/arch/arm64/boot/dts/qcom/sm8350.dtsi
> > > index 7e585d9e4c68..8547c0b2f060 100644
> > > --- a/arch/arm64/boot/dts/qcom/sm8350.dtsi
> > > +++ b/arch/arm64/boot/dts/qcom/sm8350.dtsi
> > > @@ -721,6 +721,9 @@ i2c14: i2c@...000 {
> > >  				pinctrl-names = "default";
> > >  				pinctrl-0 = <&qup_i2c14_default>;
> > >  				interrupts = <GIC_SPI 373 IRQ_TYPE_LEVEL_HIGH>;
> > > +				dmas = <&gpi_dma2 0 0 QCOM_GPI_I2C>,
> > > +				       <&gpi_dma2 1 0 QCOM_GPI_I2C>;
> > > +				dma-names = "tx", "rx";
> > 
> > I have been thinking about this. I dont feel this is right approach here
> > as this is board dependent and having the firmware loaded on the board..
> > 
> > This was tested on HDK and can fail in MTP or other boards.. which might
> > be in FIFO mode
> > 
> 
> But if the controller is in FIFO mode, then !fifo_disable so we wouldn't
> try to pick up the dmas. And in the opposite case, i.e. when
> fifo_disable, the introduction of the GPI implementation meant that the
> i2c driver wouldn't no longer probe without the dmas specified.
> 
> Unfortunately we don't have any i2c busses enabled on the MTP currently,
> so I'm not able to validate this easily.
> 
> 
> For the SPI driver though, the same logic is used to invoke
> spi_geni_grab_gpi_chan(). So dmas will only be considered if
> fifo_disabled is set.

Right, I tested that and it works just fine. So lets go ahead with this
approach

> That said, in the even that the SPI driver finds a fifo_disabled
> controller and dma_request_chan() returns an error, we will fall back to
> fifo mode instead. I'm not sure if that's desirable...

I agree, we should not fall back, that does not make sense at all

-- 
~Vinod