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

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Date: Wed, 22 May 2024 08:49:43 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Luca Weiss <luca@...tu.xyz>, Rob Herring <robh@...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 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?


Best regards,
Krzysztof