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Message-ID: <e4579702-089e-48cb-bf06-f8e4fb618050@kernel.org>
Date: Thu, 23 May 2024 08:19:11 +0200
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Subject: Re: [PATCH RFC 1/2] dt-bindings: soc: qcom,smsm: Allow specifying
 mboxes instead of qcom,ipc
To: Luca Weiss <luca@z3ntu.xyz>, Rob Herring <robh@kernel.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Cc: ~postmarketos/upstreaming@lists.sr.ht, phone-devel@vger.kernel.org,
 Bjorn Andersson <andersson@kernel.org>,
 Konrad Dybcio <konrad.dybcio@linaro.org>,
 Krzysztof Kozlowski <krzk+dt@kernel.org>, Conor Dooley
 <conor+dt@kernel.org>, Andy Gross <agross@kernel.org>,
 linux-arm-msm@vger.kernel.org, devicetree@vger.kernel.org,
 linux-kernel@vger.kernel.org
References: <20240424-smsm-mbox-v1-0-555f3f442841@z3ntu.xyz>
 <6253429.lOV4Wx5bFT@g550jk> <aced3d43-5f79-4b57-8663-5762db1ad2f6@linaro.org>
 <5099926.GXAFRqVoOG@g550jk>
From: Krzysztof Kozlowski <krzk@kernel.org>
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In-Reply-To: <5099926.GXAFRqVoOG@g550jk>
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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>

> 
> And my point is that I'm not sure if any platform will ever need ipc-0, but
> the code to use that if it ever exists is there - the driver always
> tries getting an mbox (currently just syscon of course) for every host
> from 0 to n.
> 
> These are the current (non-mbox-API) mboxes provided to smsm:
> 
> $ git grep qcom,ipc- arch/
> arch/arm/boot/dts/qcom/qcom-apq8064.dtsi:               qcom,ipc-1 = <&l2cc 8 4>;
> arch/arm/boot/dts/qcom/qcom-apq8064.dtsi:               qcom,ipc-2 = <&l2cc 8 14>;
> arch/arm/boot/dts/qcom/qcom-apq8064.dtsi:               qcom,ipc-3 = <&l2cc 8 23>;
> arch/arm/boot/dts/qcom/qcom-apq8064.dtsi:               qcom,ipc-4 = <&sps_sic_non_secure 0x4094 0>;
> arch/arm/boot/dts/qcom/qcom-msm8974.dtsi:               qcom,ipc-1 = <&apcs 8 13>;
> arch/arm/boot/dts/qcom/qcom-msm8974.dtsi:               qcom,ipc-2 = <&apcs 8 9>;
> arch/arm/boot/dts/qcom/qcom-msm8974.dtsi:               qcom,ipc-3 = <&apcs 8 19>;
> arch/arm64/boot/dts/qcom/msm8916.dtsi:          qcom,ipc-1 = <&apcs 8 13>;
> arch/arm64/boot/dts/qcom/msm8916.dtsi:          qcom,ipc-3 = <&apcs 8 19>;
> arch/arm64/boot/dts/qcom/msm8939.dtsi:          qcom,ipc-1 = <&apcs1_mbox 8 13>;
> arch/arm64/boot/dts/qcom/msm8939.dtsi:          qcom,ipc-3 = <&apcs1_mbox 8 19>;
> arch/arm64/boot/dts/qcom/msm8953.dtsi:          qcom,ipc-1 = <&apcs 8 13>;
> arch/arm64/boot/dts/qcom/msm8953.dtsi:          qcom,ipc-3 = <&apcs 8 19>;
> arch/arm64/boot/dts/qcom/msm8976.dtsi:          qcom,ipc-1 = <&apcs 8 13>;
> arch/arm64/boot/dts/qcom/msm8976.dtsi:          qcom,ipc-2 = <&apcs 8 9>;
> arch/arm64/boot/dts/qcom/msm8976.dtsi:          qcom,ipc-3 = <&apcs 8 19>;
> 
>>
>> mboxes = <&apcs 13>, <&apcs 9>, <&apcs 19>;

So which case is not covered?

Best regards,
Krzysztof