linux-kernel - Re: [RFC 0/3] Enable firmware-managed USB resources on Qcom targets

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Message-ID: <1a47c20a-abda-4493-a8f0-ff7b4e144d9c@quicinc.com>
Date: Tue, 5 Mar 2024 23:34:12 +0530
From: Sriram Dash <quic_sriramd@...cinc.com>
To: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        <andersson@...nel.org>, <konrad.dybcio@...aro.org>, <vkoul@...nel.org>,
        <kishon@...nel.org>, <robh@...nel.org>,
        <krzysztof.kozlowski+dt@...aro.org>, <conor+dt@...nel.org>,
        <gregkh@...uxfoundation.org>, <quic_wcheng@...cinc.com>,
        <Thinh.Nguyen@...opsys.com>, <p.zabel@...gutronix.de>,
        <linux-arm-msm@...r.kernel.org>, <linux-phy@...ts.infradead.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-usb@...r.kernel.org>, <quic_psodagud@...cinc.com>,
        <quic_nkela@...cinc.com>, <manivannan.sadhasivam@...aro.org>,
        <ulf.hansson@...aro.org>, <sudeep.holla@....com>,
        <quic_shazhuss@...cinc.com>
Subject: Re: [RFC 0/3] Enable firmware-managed USB resources on Qcom targets

On 3/5/2024 10:42 PM, Krzysztof Kozlowski wrote:
> On 05/03/2024 17:57, Sriram Dash wrote:
>> Some target systems allow multiple resources to be managed by firmware.
> 
> Which? Why this is so vague...
> 

SA8775 will be using it as pilot. Will include the target name.

>> On these targets, tasks related to clocks, regulators, resets, and
>> interconnects can be delegated to the firmware, while the remaining
>> responsibilities are handled by Linux.
>>
>> To support the management of partial resources in Linux and leave the rest
>> to firmware, multiple power domains are introduced. Each power domain can
>> manage one or more resources, depending on the specific use case.
>>
>> These power domains handle SCMI calls to the firmware, enabling the
>> activation and deactivation of firmware-managed resources.
>>
>> The driver is responsible for managing multiple power domains and
>> linking them to consumers as needed. Incase there is only single
>> power domain, it is considered to be a standard GDSC hooked on to
>> the qcom dt node which is read and assigned to device structure
>> (by genpd framework) before the driver probe even begins.
> 
> This will break the ABI. Sorry, come with an ABI stable solution.
> 

The plan is to include multiple power-domains and fw-managed
property or similar in the device tree and fw-managed property
will be deciding if we need some resource management offloaded
to firmware. So, OS is always in control here. The decision
making will be done in the drivers. Also, there will be no
separate vendor hooks.

> Best regards,
> Krzysztof
>