linux-kernel - Re: [PATCH net-next v2 3/4] dt-bindings: net: Add schema for Qualcomm BAM-DMUX

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Date:   Tue, 19 Oct 2021 15:31:04 +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 <netdev@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        "open list:DMA GENERIC OFFLOAD ENGINE SUBSYSTEM" 
        <dmaengine@...r.kernel.org>, devicetree@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        phone-devel@...r.kernel.org,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS
        <devicetree@...r.kernel.org>, Hans de Goede <hdegoede@...hat.com>, Andy
        Shevchenko <andy.shevchenko@...il.com>," 
        <~postmarketos/upstreaming@...ts.sr.ht>,
        Jeffrey Hugo <jeffrey.l.hugo@...il.com>
Subject: Re: [PATCH net-next v2 3/4] dt-bindings: net: Add schema for
 Qualcomm BAM-DMUX

On Tue, Oct 19, 2021 at 08:19:42AM -0500, Rob Herring wrote:
> On Tue, Oct 19, 2021 at 2:03 AM Stephan Gerhold <stephan@...hold.net> wrote:
> >
> > On Mon, Oct 18, 2021 at 03:22:25PM -0500, Rob Herring wrote:
> > > On Mon, Oct 11, 2021 at 04:17:35PM +0200, Stephan Gerhold wrote:
> > > > The BAM Data Multiplexer provides access to the network data channels of
> > > > modems integrated into many older Qualcomm SoCs, e.g. Qualcomm MSM8916 or
> > > > MSM8974. It is built using a simple protocol layer on top of a DMA engine
> > > > (Qualcomm BAM) and bidirectional interrupts to coordinate power control.
> > > >
> > > > The device tree node combines the incoming interrupt with the outgoing
> > > > interrupts (smem-states) as well as the two DMA channels, which allows
> > > > the BAM-DMUX driver to request all necessary resources.
> > > >
> > > > Signed-off-by: Stephan Gerhold <stephan@...hold.net>
> > > > ---
> > > > Changes since RFC: None.
> > > > ---
> > > >  .../bindings/net/qcom,bam-dmux.yaml           | 87 +++++++++++++++++++
> > > >  1 file changed, 87 insertions(+)
> > > >  create mode 100644 Documentation/devicetree/bindings/net/qcom,bam-dmux.yaml
> > > >
> > > > diff --git a/Documentation/devicetree/bindings/net/qcom,bam-dmux.yaml b/Documentation/devicetree/bindings/net/qcom,bam-dmux.yaml
> > > > new file mode 100644
> > > > index 000000000000..33e125e70cb4
> > > > --- /dev/null
> > > > +++ b/Documentation/devicetree/bindings/net/qcom,bam-dmux.yaml
> > > > @@ -0,0 +1,87 @@
> > > > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > > > +%YAML 1.2
> > > > +---
> > > > +$id: http://devicetree.org/schemas/net/qcom,bam-dmux.yaml#
> > > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > > +
> > > > +title: Qualcomm BAM Data Multiplexer
> > > > +
> > > > +maintainers:
> > > > +  - Stephan Gerhold <stephan@...hold.net>
> > > > +
> > > > +description: |
> > > > +  The BAM Data Multiplexer provides access to the network data channels
> > > > +  of modems integrated into many older Qualcomm SoCs, e.g. Qualcomm MSM8916
> > > > +  or MSM8974. It is built using a simple protocol layer on top of a DMA engine
> > > > +  (Qualcomm BAM DMA) and bidirectional interrupts to coordinate power control.
> > > > +
> > > > +properties:
> > > > +  compatible:
> > > > +    const: qcom,bam-dmux
> > >
> > > Is this block the same on every SoC? It needs to be SoC specific.
> > >
> >
> > Hm, I think describing it as *SoC*-specific wouldn't be accurate:
> > This node does not describe any hardware block, it's more a "firmware
> > convention". The only hardware involved is the BAM DMA engine, which
> > already has SoC/IP-specific compatibles in its own device tree node.
> >
> > This means that if anything there should be "firmware version"-specific
> > compatibles, because one SoC might have different (typically signed)
> > firmware versions that provide slightly different functionality.
> > However, I have to admit that I'm not familiar enough with the different
> > firmware versions to come up with a reasonable naming schema for the
> > compatible. :/
> >
> > In general, I cannot think of any difference between different versions
> > that would matter to a driver. The protocol is quite simple, and minor
> > firmware differences can be better handled through the control channel
> > that sets up the connection for the modem.
> >
> > Does that make sense?
> 
> Okay. Please add some of the above details to the binding.
> 

OK, I will try to clarify this a bit in v3.

Thanks!
Stephan