linux-kernel - Re: [RFC PATCH net-next 1/4] dt-bindings: dmaengine: bam

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Date:   Thu, 29 Jul 2021 21:50:54 +0200
From:   Stephan Gerhold <stephan@...hold.net>
To:     Rob Herring <robh@...nel.org>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Loic Poulain <loic.poulain@...aro.org>,
        Sergey Ryazanov <ryazanov.s.a@...il.com>,
        Johannes Berg <johannes@...solutions.net>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Andy Gross <agross@...nel.org>, Vinod Koul <vkoul@...nel.org>,
        Aleksander Morgado <aleksander@...ksander.es>,
        netdev@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        dmaengine@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, phone-devel@...r.kernel.org,
        ~postmarketos/upstreaming@...ts.sr.ht,
        Jeffrey Hugo <jeffrey.l.hugo@...il.com>
Subject: Re: [RFC PATCH net-next 1/4] dt-bindings: dmaengine: bam_dma: Add
 remote power collapse mode

On Thu, Jul 29, 2021 at 01:36:31PM -0600, Rob Herring wrote:
> On Mon, Jul 19, 2021 at 04:53:14PM +0200, Stephan Gerhold wrote:
> > In some configurations, the BAM DMA controller is set up by a remote
> > processor and the local processor can simply start making use of it
> > without setting up the BAM. This is already supported using the
> > "qcom,controlled-remotely" property.
> > 
> > However, for some reason another possible configuration is that the
> > remote processor is responsible for powering up the BAM, but we are
> > still responsible for initializing it (e.g. resetting it etc). Add
> > a "qcom,remote-power-collapse" property to describe that configuration.
> > 
> > Signed-off-by: Stephan Gerhold <stephan@...hold.net>
> > ---
> > NOTE: This is *not* a compile-time requirement for the BAM-DMUX driver
> >       so this could also go through the dmaengine tree.
> > 
> > Also note that there is an ongoing effort to convert these bindings
> > to DT schema but sadly there were not any updates for a while. :/
> > https://lore.kernel.org/linux-arm-msm/20210519143700.27392-2-bhupesh.sharma@linaro.org/
> > ---
> >  Documentation/devicetree/bindings/dma/qcom_bam_dma.txt | 2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff --git a/Documentation/devicetree/bindings/dma/qcom_bam_dma.txt b/Documentation/devicetree/bindings/dma/qcom_bam_dma.txt
> > index cf5b9e44432c..362a4f0905a8 100644
> > --- a/Documentation/devicetree/bindings/dma/qcom_bam_dma.txt
> > +++ b/Documentation/devicetree/bindings/dma/qcom_bam_dma.txt
> > @@ -15,6 +15,8 @@ Required properties:
> >    the secure world.
> >  - qcom,controlled-remotely : optional, indicates that the bam is controlled by
> >    remote proccessor i.e. execution environment.
> > +- qcom,remote-power-collapse : optional, indicates that the bam is powered up by
> > +  a remote processor but must be initialized by the local processor.
> 
> Wouldn't 'qcom,remote-power' or 'qcom,remote-powered' be sufficient? I 
> don't understand what 'collapse' means here. Doesn't sound good though.
> 

Yeah I can't think of any significant meaning of the "collapse" part
for the bindings, I probably just picked it up somewhere while trying to
find some information about how the BAM DMUX setup works. :)

Just one question, would you prefer "qcom,remote-powered" or rather
"qcom,powered-remotely" for consistency with the existing
"qcom,controlled-remotely"? Both sounds fine to me.

Thanks!
Stephan