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

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Date: Sat, 25 May 2024 18:47:08 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Luca Weiss <luca@...tu.xyz>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
 ~postmarketos/upstreaming@...ts.sr.ht
Cc: 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 24/05/2024 19:55, Luca Weiss wrote:
> On Donnerstag, 23. Mai 2024 08:19:11 MESZ Krzysztof Kozlowski wrote:
>> On 23/05/2024 08:16, Luca Weiss wrote:
>>> 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.
>>
>> ? You can list it, what's the problem>
> 
> Maybe we're talking past each other...
> 
> You asked why this wouldn't work:
> 
>   e.g. for ipc-1, ipc-2 and ipc-4 (so no ipc-0 and ipc-3):
>   mboxes = <&apcs 13>, <&apcs 9>, <&apcs 19>;
> 
> How would we know that the 3rd mailbox (&apcs 19) is for the 4th host
> (previous ipc-4)?
> 
> 1. If we use mboxes with indexes we'd need to have <0> values for
> "smsm hosts" where we don't have a mailbox for - this is at least
> for the 2nd smsm host (qcom,ipc-2) for a bunch of SoCs.
> 
> 2. If we use mboxes with mbox-names then we could skip that since we
> can directly specify which "smsm host" a given mailbox is for.
> 
> My only question really is whether 1. or 2. is a better idea.
> 
> Is this clearer now or still not?


So again, does the driver care about missing entry? If so, why?

Best regards,
Krzysztof