linux-kernel - Re: [PATCH RFC 1/2] dt-bindings: soc: qcom,smsm: Allow specifying mboxes instead of qcom,ipc

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Date: Thu, 23 May 2024 08:16:17 +0200
From: Luca Weiss <luca@...tu.xyz>
To: Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk@...nel.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc: ~postmarketos/upstreaming@...ts.sr.ht, phone-devel@...r.kernel.org,
 Bjorn Andersson <andersson@...nel.org>,
 Konrad Dybcio <konrad.dybcio@...aro.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>,
 Andy Gross <agross@...nel.org>, linux-arm-msm@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject:
 Re: [PATCH RFC 1/2] dt-bindings: soc: qcom,smsm: Allow specifying mboxes
 instead of qcom,ipc

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.

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>;
> 
> Best regards,
> Krzysztof
> 
>