linux-kernel - Re: [RFC 1/7] dt-bindings: mailbox: qcom: Add CPUCP mailbox controller bindings

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Message-ID: <2b437106-2ae4-bfb2-3ca5-c603d0cf4e2f@quicinc.com>
Date: Mon, 12 Feb 2024 11:18:14 +0530
From: Sibi Sankar <quic_sibis@...cinc.com>
To: Konrad Dybcio <konrad.dybcio@...aro.org>, <sudeep.holla@....com>,
        <cristian.marussi@....com>, <andersson@...nel.org>,
        <jassisinghbrar@...il.com>, <robh+dt@...nel.org>,
        <krzysztof.kozlowski+dt@...aro.org>
CC: <linux-kernel@...r.kernel.org>, <linux-arm-msm@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <quic_rgottimu@...cinc.com>,
        <quic_kshivnan@...cinc.com>, <conor+dt@...nel.org>
Subject: Re: [RFC 1/7] dt-bindings: mailbox: qcom: Add CPUCP mailbox
 controller bindings



On 2/9/24 04:44, Konrad Dybcio wrote:
> On 8.02.2024 11:22, Sibi Sankar wrote:
>>
>>
>> On 1/18/24 01:23, Konrad Dybcio wrote:
>>>
>>>
>>> On 1/17/24 18:34, Sibi Sankar wrote:
>>>> Add devicetree binding for CPUSS Control Processor (CPUCP) mailbox
>>>> controller.
>>>>
>>>> Signed-off-by: Sibi Sankar <quic_sibis@...cinc.com>
>>>> ---
>>>
>>
>> Hey Konrad,
>>
>> Thanks for taking time to review the series.
>>
>>> [...]
>>>
>>>> +  - |
>>>> +    #include <dt-bindings/interrupt-controller/arm-gic.h>
>>>> +
>>>> +    mailbox@...30000 {
>>>> +        compatible = "qcom,x1e80100-cpucp-mbox", "qcom,cpucp-mbox";
>>>> +        reg = <0x17430000 0x10000>, <0x18830000 0x300>;
>>>
>>> These reg spaces are quite far apart.. On 7280-8550, a similar
>>> mailbox exists, although it's dubbed RIMPS-mbox instead. In
>>> that case, I separated the mbox into tx (via
>>> qcom-apcs-ipc-mailbox.c) and rx (with a simple driver). Still
>>> haven't pushed or posted that anywhere, I'd need to access
>>> another machine..
>>>
>>> On (some of) these SoCs, one of the channels (rx[1], iirc?) clearly
>>> bleeds into the CPUFREQ_HW/OSM register region, which gives an
>>> impression of misrepresenting the hardware. X1E doesn't have a
>>> node for cpufreq_hw defined, so I can't tell whether it's also the
>>> case here.
>>
>> I am aware of ^^ discussion and the X1E doesn't have this problem.
>> Both the regions described are only used for mailbox communication.
>> X1E uses the scmi perf protocol for cpu dvfs.
> 
> Yes, that's clear.
> 
> I am however asking for something different: I presume the CPUSS
> IP hasn't changed too much on this SoC, other than having new cores and
> OSM now being controlled through a different firmware interface, and I'd
> like to keep the hardware description in our DT as close to the metal as
> possible.
> 
> In other words, if the good ol' OSM hardware is indeed there under however
> many layers of firmware, and if RX does indeed bleed into its register
> space, I'd prefer there be at least a syscon node describing the actual
> block, and not a magic hwio entry that's many zeroes away.
> 

With the new cores X1E does not have any artifacts from the legacy
OSM way that Qualcomm has followed till now. If it indeed existed it
would make zero sense to vote for CPU frequencies through a mailbox than
vote for it directly.

-Sibi

> Konrad
>