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Message-ID: <88de471c-a2e2-008a-fb9b-b8039b018209@quicinc.com>
Date:   Mon, 31 Jul 2023 07:04:26 -0700
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Subject: Re: [PATCH v2 3/3] firmware: arm_scmi: Add qcom hvc/shmem transport
From:   Nikunj Kela <quic_nkela@quicinc.com>
To:     Cristian Marussi <cristian.marussi@arm.com>
CC:     <sudeep.holla@arm.com>, <robh+dt@kernel.org>,
        <krzysztof.kozlowski+dt@linaro.org>, <conor+dt@kernel.org>,
        <agross@kernel.org>, <andersson@kernel.org>,
        <konrad.dybcio@linaro.org>, <linux-arm-kernel@lists.infradead.org>,
        <devicetree@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        <linux-arm-msm@vger.kernel.org>
References: <20230718160833.36397-1-quic_nkela@quicinc.com>
 <20230724164419.16092-1-quic_nkela@quicinc.com>
 <20230724164419.16092-4-quic_nkela@quicinc.com> <ZMAASCqwMbqX7T7L@pluto>
 <fc42e319-0ead-db94-9335-e07ff780dfa2@quicinc.com>
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On 7/25/2023 10:12 AM, Nikunj Kela wrote:
>
> On 7/25/2023 10:03 AM, Cristian Marussi wrote:
>> On Mon, Jul 24, 2023 at 09:44:19AM -0700, Nikunj Kela wrote:
>>> Add a new transport channel to the SCMI firmware interface driver for
>>> SCMI message exchange on Qualcomm virtual platforms.
>>>
>>> The hypervisor associates an object-id also known as capability-id
>>> with each hvc doorbell object. The capability-id is used to identify 
>>> the
>>> doorbell from the VM's capability namespace, similar to a 
>>> file-descriptor.
>>>
>>> The hypervisor, in addition to the function-id, expects the 
>>> capability-id
>>> to be passed in x1 register when HVC call is invoked.
>>>
>>> The qcom hvc doorbell/shared memory transport uses a statically defined
>>> shared memory region that binds with "arm,scmi-shmem" device tree node.
>>>
>>> The function-id & capability-id are allocated by the hypervisor on 
>>> bootup
>>> and are stored in the shmem region by the firmware before starting 
>>> Linux.
>>>
>>> Currently, there is no usecase for the atomic support therefore this 
>>> driver
>>> doesn't include the changes for the same.
>>>
>> Hi Nikunj,
>>
>> so basically this new SCMI transport that you are introducing is just
>> exactly like the existing SMC transport with the only difference that
>> you introduced even another new way to configure func_id, a new cap_id
>> param AND the fact that you use HVC instead of SMC... all of this tied
>> to a new compatible to identify this new transport mechanism....
>> ..but all in all is just a lot of plain duplicated code to maintain...
>>
>> ...why can't you fit this other smc/hvc transport variant into the
>> existing SMC transport by properly picking and configuring 
>> func_id/cap_id
>> and "doorbell" method (SMC vs HVC) in the chan_setup() step ?
>>
>> ..I mean ... you can decide where to pick your params based on
>> compatibles and also you can setup your invokation method (SMC vs HVC)
>> based on those...while keeping all the other stuff exactly the same...
>> ...including support for atomic exchanges...if not, when you'll need 
>> that
>> too in your QC_HVC transport you'll have to duplicate also that (and my
>> bugs too probably :P)
>>
>> (... well maybe in this scenario also the transport itself should be
>> renamed from SMC to something more general...)
>>
>> Not sure if I am missing something, or if Sudeep will be horrified by
>> this unifying proposal of mine, but in this series as it stands now I
>> just see a lot of brutally duplicated stuff that just differs by naming
>> and a very minimal change in logic that could be addressed changing and
>> generalizing the original SMC transport code instead.
>>
>> Thanks,
>> Cristian
>
> Hi Christian,
>
> I totally agree with you and will be happy to include my changes in 
> smc.c if Sudeep agrees with that approach.
>
> Thanks

Hi Sudeep, Could you please provide your feedback on this? Thanks