linux-kernel - Re: [PATCH 1/2] dt-bindings: misc: qcom,fastrpc: add qcom,assign-all-memory property

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Message-ID: <CAA8EJprxn6LSDu3NV8r0pFr1pc+zRydoyOdJ2y6VRN3zZ8a52g@mail.gmail.com>
Date:   Mon, 27 Mar 2023 17:32:30 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Dylan Van Assche <me@...anvanassche.be>
Cc:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Amol Maheshwari <amahesh@....qualcomm.com>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        ~postmarketos/upstreaming@...ts.sr.ht, phone-devel@...r.kernel.org
Subject: Re: [PATCH 1/2] dt-bindings: misc: qcom,fastrpc: add
 qcom,assign-all-memory property

On Mon, 27 Mar 2023 at 17:27, Dylan Van Assche <me@...anvanassche.be> wrote:
>
> Hi Krzysztof,
>
> On Mon, 2023-03-27 at 14:22 +0200, Krzysztof Kozlowski wrote:
> > On 27/03/2023 13:37, Dylan Van Assche wrote:
> > > Hi Krzysztof,
> > >
> > > On Sun, 2023-03-26 at 10:55 +0200, Krzysztof Kozlowski wrote:
> > > > On 25/03/2023 14:44, Dylan Van Assche wrote:
> > > > > Document the added qcom,assign-all-memory in devicetree
> > > > > bindings.
> > > > >
> > > > > Signed-off-by: Dylan Van Assche <me@...anvanassche.be>
> > > > > ---
> > > > >  Documentation/devicetree/bindings/misc/qcom,fastrpc.yaml | 6
> > > > > ++++++
> > > > >  1 file changed, 6 insertions(+)
> > > > >
> > > > > diff --git
> > > > > a/Documentation/devicetree/bindings/misc/qcom,fastrpc.yaml
> > > > > b/Documentation/devicetree/bindings/misc/qcom,fastrpc.yaml
> > > > > index 1ab9588cdd89..fa5b00534b30 100644
> > > > > --- a/Documentation/devicetree/bindings/misc/qcom,fastrpc.yaml
> > > > > +++ b/Documentation/devicetree/bindings/misc/qcom,fastrpc.yaml
> > > > > @@ -57,6 +57,12 @@ properties:
> > > > >        Virtual machine IDs for remote processor.
> > > > >      $ref: "/schemas/types.yaml#/definitions/uint32-array"
> > > > >
> > > > > +  qcom,assign-all-mem:
> > > > > +    description:
> > > > > +      Assign memory to all Virtual machines defined by
> > > > > qcom,vmids.
> > > >
> > > > This (neither commit msg) does not explain why this is needed and
> > > > actually does not sound like hardware-related property.
> > >
> > > This is made a separate property to toggle different behavior in
> > > the
> > > driver if it is needed for some FastRPC nodes.
> >
> > Bindings are not for driver behavior.
> >
> > > Downstream does guard
> > > this with a property 'restrict-access' as well, see [1] for a
> > > random
> > > SDM845 downstream kernel. On SDM845, this property is not present,
> > > thus
> > > the IF block runs. On SDM670, this property is present, then the IF
> > > block is skipped. That's why I opt for this property to have this
> > > behaviour conditionally. I'm not sure how to explain it better
> > > though.
> >
> > Still you described driver... Please come with something more
> > hardware
> > related.
>
> So just updating the description is enough then?
>
> As this is all reverse engineered, I have no access to the
> documentation of FastRPC, so best effort:

Vendor kernels put a lot of controls into DT, despite some of these
controls being related to software or being a platform constant.
Upstream tends to push some of the constraints into the driver data,
leaving only variadic parts in DT.
Could you please check if the property you are proposing is constant
among the devices on a platform or not. If it is a platform
peculiarity, a usual way is to add it to driver data rather than the
DT.

>
> """
> Mark allocated memory region accessible to remote processor.
> This memory region is used by remote processor to communicate
> when no dedicated Fastrpc context bank hardware is available
> for remote processor.
> """
>
> Is this the description that is 'more hardware related'?

-- 
With best wishes
Dmitry