RE: [PATCH V6 3/5] PCI: thunder-pem: Allow to probe PEM-specific register range for ACPI case

[Gabriele Paoloni <gabriele.paoloni@huawei.com>]

Hi Bjorn

> -----Original Message-----
> From: Bjorn Helgaas [mailto:helgaas@kernel.org]
> Sent: 21 September 2016 19:59
> To: Gabriele Paoloni
> Cc: Ard Biesheuvel; Tomasz Nowicki; David Daney; Will Deacon; Catalin
> Marinas; Rafael Wysocki; Lorenzo Pieralisi; Arnd Bergmann; Hanjun Guo;
> Sinan Kaya; Jayachandran C; Christopher Covington; Duc Dang; Robert
> Richter; Marcin Wojtas; Liviu Dudau; Wangyijing; Mark Salter; linux-
> pci@vger.kernel.org; linux-arm-kernel@lists.infradead.org; Linaro ACPI
> Mailman List; Jon Masters; Andrea Gallo; Jeremy Linton; liudongdong
> (C); Jeff Hugo; linux-acpi@vger.kernel.org; linux-
> kernel@vger.kernel.org; Rafael J. Wysocki
> Subject: Re: [PATCH V6 3/5] PCI: thunder-pem: Allow to probe PEM-
> specific register range for ACPI case
> 
> On Wed, Sep 21, 2016 at 02:10:55PM +0000, Gabriele Paoloni wrote:
> > Hi Bjorn
> >
> > [...]
> >
> >
> > >
> > > If future hardware is completely ECAM-compliant and we don't need
> any
> > > more MCFG quirks, that would be great.
> > >
> > > But we'll still need to describe that memory-mapped config space
> > > somewhere.  If that's done with PNP0C02 or similar devices (as is
> done
> > > on my x86 laptop), we'd be all set.
> > >
> > > If we need to work around firmware in the field that doesn't do
> that,
> > > one possibility is a PNP quirk along the lines of
> > > quirk_amd_mmconfig_area().
> >
> > So, if my understanding is correct, for platforms that have not been
> > shipped yet you propose to use PNP0C02 in the ACPI table in order to
> > declare a motherboard reserved resource whereas for shipped platforms
> > you propose to have a quirk along pnp_fixups in order to track the
> > resource usage even if values are hardcoded...correct?
> 
> Yes.  I'm open to alternate proposals, but x86 uses PNP0C02, and
> following existing practice seems reasonable.
> 
> > Before Tomasz came up with this patchset we had a call between the
> vendors
> > involved in this PCI quirks saga and other guys from Linaro and ARM.
> >
> > Lorenzo summarized the outcome as in the following link
> > http://lkml.iu.edu/hypermail/linux/kernel/1606.2/03344.html
> >
> > Since this quirks mechanism has been discussed for quite a long time
> now
> > IMHO it would be good to have a last call including also you (Bjorn)
> so
> > that we can all agree on what to do and we avoid changing our drivers
> again
> > and again...
> 
> I think we're converging pretty fast.  As far as I'm concerned, the
> v6 ECAM quirks implementation is perfect.  The only remaining issue is
> reporting the ECAM resources, and I haven't seen objections to using
> PNP0C02 + PNP quirks for broken firmware.
> 
> There is the question of how or whether to associate a PNP0A03 PCI
> bridge with resources from a different PNP0C02 device, but that's not
> super important.  If the hard-coded resources appear both in a quirk
> and in the PCI bridge driver, it's ugly but not the end of the world.
> We've still achieved the objective of avoiding landmines in the
> address space.

Ok got it many thanks

Gab

> 
> Bjorn