Received-SPF: pass (google.com: domain of linux-kernel+bounces-188985-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.80.249 as permitted sender) client-ip=147.75.80.249;
From: Luca Weiss <luca@z3ntu.xyz>
To: Rob Herring <robh@kernel.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>,
 ~postmarketos/upstreaming@lists.sr.ht
Cc: ~postmarketos/upstreaming@lists.sr.ht, phone-devel@vger.kernel.org,
 Bjorn Andersson <andersson@kernel.org>,
 Konrad Dybcio <konrad.dybcio@linaro.org>,
 Krzysztof Kozlowski <krzk+dt@kernel.org>, Conor Dooley <conor+dt@kernel.org>,
 Andy Gross <agross@kernel.org>, linux-arm-msm@vger.kernel.org,
 devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
 Krzysztof Kozlowski <krzk@kernel.org>
Subject:
 Re: [PATCH RFC 1/2] dt-bindings: soc: qcom,smsm: Allow specifying mboxes
 instead of qcom,ipc
Date: Fri, 24 May 2024 19:55:19 +0200
Message-ID: <4881282.LvFx2qVVIh@g550jk>
In-Reply-To: <e4579702-089e-48cb-bf06-f8e4fb618050@kernel.org>
References:
 <20240424-smsm-mbox-v1-0-555f3f442841@z3ntu.xyz> <5099926.GXAFRqVoOG@g550jk>
 <e4579702-089e-48cb-bf06-f8e4fb618050@kernel.org>
Precedence: bulk
MIME-Version: 1.0
Content-Transfer-Encoding: 7Bit
Content-Type: text/plain; charset="utf-8"

On Donnerstag, 23. Mai 2024 08:19:11 MESZ Krzysztof Kozlowski wrote:
> On 23/05/2024 08:16, Luca Weiss wrote:
> > On Donnerstag, 23. Mai 2024 08:02:13 MESZ Krzysztof Kozlowski wrote:
> >> On 22/05/2024 19:34, Luca Weiss wrote:
> >>> On Mittwoch, 22. Mai 2024 08:49:43 MESZ Krzysztof Kozlowski wrote:
> >>>> On 21/05/2024 22:35, Luca Weiss wrote:
> >>>>> On Dienstag, 21. Mai 2024 10:58:07 MESZ Krzysztof Kozlowski wrote:
> >>>>>> On 20/05/2024 17:11, Luca Weiss wrote:
> >>>>>>> Hi Krzysztof
> >>>>>>>
> >>>>>>> Ack, sounds good.
> >>>>>>>
> >>>>>>> Maybe also from you, any opinion between these two binding styles?
> >>>>>>>
> >>>>>>> So first using index of mboxes for the numbering, where for the known
> >>>>>>> usages the first element (and sometimes the 3rd - ipc-2) are empty <>.
> >>>>>>>
> >>>>>>> The second variant is using mbox-names to get the correct channel-mbox
> >>>>>>> mapping.
> >>>>>>>
> >>>>>>> -               qcom,ipc-1 = <&apcs 8 13>;
> >>>>>>> -               qcom,ipc-2 = <&apcs 8 9>;
> >>>>>>> -               qcom,ipc-3 = <&apcs 8 19>;
> >>>>>>> +               mboxes = <0>, <&apcs 13>, <&apcs 9>, <&apcs 19>;
> >>>>>>>
> >>>>>>> vs.
> >>>>>>>
> >>>>>>> -               qcom,ipc-1 = <&apcs 8 13>;
> >>>>>>> -               qcom,ipc-2 = <&apcs 8 9>;
> >>>>>>> -               qcom,ipc-3 = <&apcs 8 19>;
> >>>>>>> +               mboxes = <&apcs 13>, <&apcs 9>, <&apcs 19>;
> >>>>>>> +               mbox-names = "ipc-1", "ipc-2", "ipc-3";
> >>>>>>
> >>>>>> Sorry, don't get, ipc-1 is the first mailbox, so why would there be <0>
> >>>>>> in first case?
> >>>>>
> >>>>> Actually not, ipc-0 would be permissible by the driver, used for the 0th host
> >>>>>
> >>>>> e.g. from:
> >>>>>
> >>>>> 	/* Iterate over all hosts to check whom wants a kick */
> >>>>> 	for (host = 0; host < smsm->num_hosts; host++) {
> >>>>> 		hostp = &smsm->hosts[host];
> >>>>>
> >>>>> Even though no mailbox is specified in any upstream dts for this 0th host I
> >>>>> didn't want the bindings to restrict that, that's why in the first example
> >>>>> there's an empty element (<0>) for the 0th smsm host
> >>>>>
> >>>>>> Anyway, the question is if you need to know that some
> >>>>>> mailbox is missing. But then it is weird to name them "ipc-1" etc.
> >>>>>
> >>>>> In either case we'd just query the mbox (either by name or index) and then
> >>>>> see if it's there? Not quite sure I understand the sentence..
> >>>>> Pretty sure either binding would work the same way.
> >>>>
> >>>> The question is: does the driver care only about having some mailboxes
> >>>> or the driver cares about each specific mailbox? IOW, is skipping ipc-0
> >>>> important for the driver?
> >>>
> >>> There's nothing special from driver side about any mailbox. Some SoCs have
> >>> a mailbox for e.g. hosts 1&2&3, some have only 1&3, and apq8064 even has
> >>> 1&2&3&4.
> >>>
> >>> And if the driver doesn't find a mailbox for a host, it just ignores it
> >>> but then of course it can't 'ring' the mailbox for that host when necessary.
> >>>
> >>> Not sure how much more I can add here, to be fair I barely understand what
> >>> this driver is doing myself apart from the obvious.
> >>
> >> From what you said, it looks like it is enough to just list mailboxes,
> >> e.g. for ipc-1, ipc-2 and ipc-4 (so no ipc-0 and ipc-3):
> > 
> > No, for sure we need also the possibility to list ipc-3.
> 
> ? You can list it, what's the problem>

Maybe we're talking past each other...

You asked why this wouldn't work:

  e.g. for ipc-1, ipc-2 and ipc-4 (so no ipc-0 and ipc-3):
  mboxes = <&apcs 13>, <&apcs 9>, <&apcs 19>;

How would we know that the 3rd mailbox (&apcs 19) is for the 4th host
(previous ipc-4)?

1. If we use mboxes with indexes we'd need to have <0> values for
"smsm hosts" where we don't have a mailbox for - this is at least
for the 2nd smsm host (qcom,ipc-2) for a bunch of SoCs.

2. If we use mboxes with mbox-names then we could skip that since we
can directly specify which "smsm host" a given mailbox is for.

My only question really is whether 1. or 2. is a better idea.

Is this clearer now or still not?


> 
> > 
> > And my point is that I'm not sure if any platform will ever need ipc-0, but
> > the code to use that if it ever exists is there - the driver always
> > tries getting an mbox (currently just syscon of course) for every host
> > from 0 to n.
> > 
> > These are the current (non-mbox-API) mboxes provided to smsm:
> > 
> > $ git grep qcom,ipc- arch/
> > arch/arm/boot/dts/qcom/qcom-apq8064.dtsi:               qcom,ipc-1 = <&l2cc 8 4>;
> > arch/arm/boot/dts/qcom/qcom-apq8064.dtsi:               qcom,ipc-2 = <&l2cc 8 14>;
> > arch/arm/boot/dts/qcom/qcom-apq8064.dtsi:               qcom,ipc-3 = <&l2cc 8 23>;
> > arch/arm/boot/dts/qcom/qcom-apq8064.dtsi:               qcom,ipc-4 = <&sps_sic_non_secure 0x4094 0>;
> > arch/arm/boot/dts/qcom/qcom-msm8974.dtsi:               qcom,ipc-1 = <&apcs 8 13>;
> > arch/arm/boot/dts/qcom/qcom-msm8974.dtsi:               qcom,ipc-2 = <&apcs 8 9>;
> > arch/arm/boot/dts/qcom/qcom-msm8974.dtsi:               qcom,ipc-3 = <&apcs 8 19>;
> > arch/arm64/boot/dts/qcom/msm8916.dtsi:          qcom,ipc-1 = <&apcs 8 13>;
> > arch/arm64/boot/dts/qcom/msm8916.dtsi:          qcom,ipc-3 = <&apcs 8 19>;
> > arch/arm64/boot/dts/qcom/msm8939.dtsi:          qcom,ipc-1 = <&apcs1_mbox 8 13>;
> > arch/arm64/boot/dts/qcom/msm8939.dtsi:          qcom,ipc-3 = <&apcs1_mbox 8 19>;
> > arch/arm64/boot/dts/qcom/msm8953.dtsi:          qcom,ipc-1 = <&apcs 8 13>;
> > arch/arm64/boot/dts/qcom/msm8953.dtsi:          qcom,ipc-3 = <&apcs 8 19>;
> > arch/arm64/boot/dts/qcom/msm8976.dtsi:          qcom,ipc-1 = <&apcs 8 13>;
> > arch/arm64/boot/dts/qcom/msm8976.dtsi:          qcom,ipc-2 = <&apcs 8 9>;
> > arch/arm64/boot/dts/qcom/msm8976.dtsi:          qcom,ipc-3 = <&apcs 8 19>;
> > 
> >>
> >> mboxes = <&apcs 13>, <&apcs 9>, <&apcs 19>;
> 
> So which case is not covered?
> 
> Best regards,
> Krzysztof
> 
>