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

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Date: Tue, 21 May 2024 22:35:22 +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 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.

Regards
Luca

> 
> Best regards,
> Krzysztof
> 
>