RE: [RFC PATCH v3 4/7] bus/cdx: add cdx-MSI domain with gic-its domain as parent

From: "Gupta, Nipun" <Nipun.Gupta@amd.com>
To: Marc Zyngier <maz@kernel.org>
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Subject: RE: [RFC PATCH v3 4/7] bus/cdx: add cdx-MSI domain with gic-its domain as parent
Date: Fri, 9 Sep 2022 06:32:39 +0000	[thread overview]
Message-ID: <DM6PR12MB3082C642F8948236AE42E07DE8439@DM6PR12MB3082.namprd12.prod.outlook.com> (raw)
In-Reply-To: <87a67aueg7.wl-maz@kernel.org>

[AMD Official Use Only - General]

> -----Original Message-----
> From: Marc Zyngier <maz@kernel.org>
> Sent: Thursday, September 8, 2022 8:00 PM
> To: Gupta, Nipun <Nipun.Gupta@amd.com>
> Cc: robh+dt@kernel.org; krzysztof.kozlowski+dt@linaro.org;
> gregkh@linuxfoundation.org; rafael@kernel.org; eric.auger@redhat.com;
> alex.williamson@redhat.com; cohuck@redhat.com; Gupta, Puneet (DCG-ENG)
> <puneet.gupta@amd.com>; song.bao.hua@hisilicon.com;
> mchehab+huawei@kernel.org; f.fainelli@gmail.com; jeffrey.l.hugo@gmail.com;
> saravanak@google.com; Michael.Srba@seznam.cz; mani@kernel.org;
> yishaih@nvidia.com; jgg@ziepe.ca; jgg@nvidia.com; robin.murphy@arm.com;
> will@kernel.org; joro@8bytes.org; masahiroy@kernel.org;
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> Harpreet <harpreet.anand@amd.com>; Agarwal, Nikhil
> <nikhil.agarwal@amd.com>; Simek, Michal <michal.simek@amd.com>;
> Radovanovic, Aleksandar <aleksandar.radovanovic@amd.com>; git (AMD-Xilinx)
> <git@amd.com>
> Subject: Re: [RFC PATCH v3 4/7] bus/cdx: add cdx-MSI domain with gic-its
> domain as parent
> 
> [CAUTION: External Email]
> 
> On Thu, 08 Sep 2022 15:13:31 +0100,
> "Gupta, Nipun" <Nipun.Gupta@amd.com> wrote:
> >
> >
> > > > +             return;
> > > > +
> > > > +     msi_domain_free_irqs(msi_domain, dev);
> > > > +}
> > > > +EXPORT_SYMBOL(cdx_msi_domain_free_irqs);
> > >
> > > This feels like a very pointless helper, and again a copy/paste from
> > > the FSL code. I'd rather you change msi_domain_free_irqs() to only
> > > take a device and use the implicit MSI domain.
> >
> > I agree with other comments except this one.
> >
> > In current implementation we have an API "cdx_msi_domain_alloc_irqs()",
> > so having "cdx_msi_domain_free_irqs()" seems legitimate, as the caller
> > would allocate and free MSI's using a similar APIs (cdx_msi_domain*).
> 
> Why would that be a problem? Using generic functions when they apply
> should be the default, and "specialised" helpers are only here as a
> reminder that our MSI API still needs serious improvement.

We can remove the wrapper API, rather have a #define to provide same name
convention for alloc and free IRQ APIs for CDX drivers. But both ways if we use
#define or direct use of msi_domain_free_irqs() API, we need
msi_domain_free_irqs() symbol exported I hope having export symbol to this
API would not be a problem.

> 
> > Changing msi_domain_free_irqs() to use implicit msi domain in case
> > msi_domain is not provided by the caller seems appropriate, Ill change the
> > same for "msi_domain_alloc_irqs()" too.
> 
> What I'm asking is that there is no explicit msi_domain anymore. We
> always use the one referenced by the device. And if that can be done
> on the allocation path too, great.

I think it can be removed from both the APIs. Also, API's
msi_domain_alloc_irqs_descs_locked() and msi_domain_free_irqs_descs_locked()
can have similar change.

> 
> > <..>
> >
> > > > diff --git a/drivers/bus/cdx/mcdi_stubs.c b/drivers/bus/cdx/mcdi_stubs.c
> > > > index cc9d30fa02f8..2c8db1f5a057 100644
> > > > --- a/drivers/bus/cdx/mcdi_stubs.c
> > > > +++ b/drivers/bus/cdx/mcdi_stubs.c
> > > > @@ -45,6 +45,7 @@ int cdx_mcdi_get_func_config(struct cdx_mcdi_t
> > > *cdx_mcdi,
> > > >       dev_params->res_count = 2;
> > > >
> > > >       dev_params->req_id = 0x250;
> > > > +     dev_params->num_msi = 4;
> > >
> > > Why the hardcoded 4? Is that part of the firmware emulation stuff?
> >
> > Yes, this is currently part of emulation, and would change with proper
> > emulation support.
> 
> What "proper emulation support"? I expect no emulation at all, but
> instead a well defined probing method.

I meant proper firmware interfacing support for probing.

> 
>         M.
> 
> --
> Without deviation from the norm, progress is not possible.