linux-kernel - Re: [PATCH 1/2] dt-bindings: ufs: qcom: allow 'dma-coherent' property

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Date:   Mon, 5 Dec 2022 19:07:12 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     Johan Hovold <johan@...nel.org>
Cc:     Johan Hovold <johan+linaro@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Alim Akhtar <alim.akhtar@...sung.com>,
        Avri Altman <avri.altman@....com>,
        Andy Gross <agross@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Bart Van Assche <bvanassche@....org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        linux-arm-msm@...r.kernel.org, linux-scsi@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] dt-bindings: ufs: qcom: allow 'dma-coherent' property

On Mon, Dec 05, 2022 at 02:12:48PM +0100, Johan Hovold wrote:
> On Mon, Dec 05, 2022 at 06:30:48PM +0530, Manivannan Sadhasivam wrote:
> > On Mon, Dec 05, 2022 at 01:27:34PM +0100, Johan Hovold wrote:
> > > On Mon, Dec 05, 2022 at 05:50:18PM +0530, Manivannan Sadhasivam wrote:
> > > > On Mon, Dec 05, 2022 at 01:07:16PM +0100, Johan Hovold wrote:
> > > > > On Mon, Dec 05, 2022 at 05:29:06PM +0530, Manivannan Sadhasivam wrote:
> > > > > > On Mon, Dec 05, 2022 at 11:08:36AM +0100, Johan Hovold wrote:
> > > > > > > UFS controllers may be cache coherent and must be marked as such in the
> > > > > > > devicetree to avoid data corruption.
> > > > > > > 
> > > > > > > This is specifically needed on recent Qualcomm platforms like SC8280XP.
> > > > > > > 
> > > > > > > Signed-off-by: Johan Hovold <johan+linaro@...nel.org>
> 
> > > > > Yes, it would be a valid, but it will only be added to the DTs of SoCs
> > > > > that actually require it. No need to re-encode the dtsi in the binding.
> > > > > 
> > > > 
> > > > But if you make a property valid in the binding then it implies that anyone
> > > > could add it to DTS which is wrong. You should make this property valid for
> > > > SoCs that actually support it.
> > > 
> > > No, it's not wrong.
> > > 
> > > Note that the binding only requires 'compatible' and 'regs', all other
> > > properties are optional, and you could, for example, add a
> > > 'reset' property to a node for a device which does not have a reset
> > > without the DT validation failing.
> > > 
> > 
> > Then what is the point of devicetree validation using bindings?
> 
> You're still making sure that no properties are added that are not
> documented, number of clocks, names of clocks, etc.
> 
> > There is also a comment from Krzysztof: https://lkml.org/lkml/2022/11/24/390
> 
> Speaking of Krzysztof:
> 
> 	https://lore.kernel.org/lkml/20221204094717.74016-5-krzysztof.kozlowski@linaro.org/
> 

Heh... I will wait for him to chime in then.

Thanks,
Mani

> Johan

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