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

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Date:   Tue, 6 Dec 2022 08:49:16 +0100
From:   Johan Hovold <johan@...nel.org>
To:     Rob Herring <robh@...nel.org>
Cc:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        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>,
        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 04:35:22PM -0600, Rob Herring wrote:
> 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.
> 
> Typically, you'd only be doing unnecessary cache flushes without it 
> rather than getting data corruption. However, it is possible this 
> property triggers other system setup or something that would cause 
> problems if not setup right.

You can end up with data corruption, for example, if the kernel remaps
a consistent buffer and writes data through the non-cacheable alias
while the coherent device snoops stale data from the caches.

Johan