linux-kernel - Re: [Nouveau] [PATCH nouveau 09/11] drm: export some variable and functions to resue the PM functions

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Message-ID: <20150106143729.GN31830@ulmo.nvidia.com>
Date:	Tue, 6 Jan 2015 15:37:30 +0100
From:	Thierry Reding <thierry.reding@...il.com>
To:	Vince Hsu <vinceh@...dia.com>
Cc:	Alexandre Courbot <gnurou@...il.com>,
	Emil Velikov <emil.l.velikov@...il.com>,
	Stephen Warren <swarren@...dotorg.org>,
	Ben Skeggs <bskeggs@...hat.com>,
	Martin Peres <martin.peres@...e.fr>,
	Roy Spliet <seven@...rod-online.com>,
	samuel.pitoiset@...il.com,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"nouveau@...ts.freedesktop.org" <nouveau@...ts.freedesktop.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [Nouveau] [PATCH nouveau 09/11] drm: export some variable and
 functions to resue the PM functions

On Tue, Jan 06, 2015 at 08:27:06PM +0800, Vince Hsu wrote:
> 
> On 01/06/2015 07:49 PM, Thierry Reding wrote:
> >* PGP Signed by an unknown key
> >
> >On Mon, Jan 05, 2015 at 08:50:18PM +0100, Alexandre Courbot wrote:
> >>On Mon, Jan 5, 2015 at 4:32 PM, Thierry Reding <thierry.reding@...il.com> wrote:
> >>>On Tue, Dec 30, 2014 at 11:18:34AM +0800, Vince Hsu wrote:
> >>>>Hi Emil,
> >>>>
> >>>>On 12/30/2014 10:34 AM, Emil Velikov wrote:
> >>>>>On 23/12/14 10:40, Vince Hsu wrote:
> >>>>>>This patch adds some checks in the suspend/resume functions to distinguish
> >>>>>>the dGPU and mobile GPU and exports some variables/functions so that the
> >>>>>>nouveau platform device can reuse them.
> >>>>>>
> >>>>>Hi Vince,
> >>>>>
> >>>>>Afaiu one needs to export a symbol as it's used by another module or
> >>>>>subsystem. With the follow up two patches you are not doing either one,
> >>>>>so I'd assume that you can just omit the EXPORT_* changes.
> >>>>The nouveau platform device driver is built as another module -
> >>>>nouveau_platform.ko. :)
> >>>I'd like to hear the opinion of the nouveau people and Alex, but I'd
> >>>very much prefer if nouveau_platform.o was simply linked into the
> >>>nouveau.ko module. I don't see any good reason to keep it separate.
> >>Yep, I agree. The decision to host platform support in a separate
> >>module looks misleaded if it results in additional exports that we
> >>would otherwise avoid. IIUC I did this to be able to use the module
> >>convenience macros to register the platform driver.
> >>
> >>>Something like the attached patch (untested) ought to do it.
> >>This patch alone won't be enough for the reason I mentioned above.
> >>However, if Vince doesn't mind handling the platform driver
> >>registration manually in nouveau_drm_init/nouveau_drm_exit, I agree
> >>this would be the way to go.
> >If we do the conversion to generic power domains, the only Tegra-
> >specific API remaining will be the access to the fuse registers for the
> >speedo value. At that point we wouldn't need the ARCH_TEGRA dependency
> >any longer and could always build the platform driver along with the PCI
> >driver.
> Do we really want the platform driver always built with the PCI driver even
> there is no dependency between them. Actually I have some patches to
> build the platform driver with !CONFIG_PCI and would like to post them maybe
> later.

I do see some advantage in making Nouveau build with !CONFIG_PCI because
it allows building the driver for an SoC without PCI. But I think always
compiling whatever is available won't hurt. Nouveau itself is rather big
(~1 MiB of text and ~120 KiB of data) whereas the platform code weighs
in at around 1.5 KiB of text and 108 B of data. I suspect that the PCI
glue is equally negligible.

Thierry

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