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: <20150106145054.GO31830@ulmo.nvidia.com>
Date:	Tue, 6 Jan 2015 15:50:56 +0100
From:	Thierry Reding <thierry.reding@...il.com>
To:	Ilia Mirkin <imirkin@...m.mit.edu>
Cc:	Vince Hsu <vinceh@...dia.com>,
	Stephen Warren <swarren@...dotorg.org>,
	"nouveau@...ts.freedesktop.org" <nouveau@...ts.freedesktop.org>,
	Emil Velikov <emil.l.velikov@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ben Skeggs <bskeggs@...hat.com>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	Roy Spliet <seven@...rod-online.com>
Subject: Re: [Nouveau] [PATCH nouveau 09/11] drm: export some variable and
 functions to resue the PM functions

On Tue, Jan 06, 2015 at 09:44:01AM -0500, Ilia Mirkin wrote:
> On Tue, Jan 6, 2015 at 9:37 AM, Thierry Reding <thierry.reding@...il.com> wrote:
> > 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.
> 
> The much bigger reductions in size would be from getting rid of all
> the stuff that's not used at all on a GK20A, like all the firmware,
> and a whole bunch of logic. I had a series that split things up into
> nv04/nv50/nvc0 categories. I believe it was considered undesirable due
> to increased build complexity. (It wasn't a nice modularized
> separation but rather just a compile-time setting.) Shouldn't be too
> hard to regenerate though.

Would you happen to remember the amount of savings for enabling only
nvc0? I'm not overly concerned with the module being 1 MiB on Tegra,
though. Most boards tend to have 2 GiB+ of memory these days and the
kernel footprint is pretty big without Nouveau anyway.

Thierry

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