Re: [PATCH v2 3/3] firmware: arm_scmi: Add qcom hvc/shmem transport

[Nikunj Kela]

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