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 08:02:13 +0200
From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To: Luca Weiss <luca@...tu.xyz>, Rob Herring <robh@...nel.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 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):

mboxes = <&apcs 13>, <&apcs 9>, <&apcs 19>;

Best regards,
Krzysztof