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

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Message-ID: <6253429.lOV4Wx5bFT@g550jk>
Date: Wed, 22 May 2024 19:34:23 +0200
From: Luca Weiss <luca@...tu.xyz>
To: Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
 Krzysztof Kozlowski <krzk@...nel.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 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.

Regards
Luca

> 
> 
> Best regards,
> Krzysztof
> 
>