Message-ID: <1343588756.1962.22.camel@shinybook.infradead.org>
Date:	Sun, 29 Jul 2012 20:05:56 +0100
From:	David Woodhouse <dwmw2@...radead.org>
To:	Andreas Heider <andreas@...tr.de>, Dave Airlie <airlied@...ux.ie>
Cc:	Matthew Garrett <mjg59@...f.ucam.org>,
	Arun Raghavan <arun.raghavan@...labora.co.uk>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] apple-gmux: Restore switch registers on suspend/resume

On Sun, 2012-07-29 at 09:46 +0200, Andreas Heider wrote:
> Am 29.07.12 03:18, schrieb David Woodhouse:
> > On Sun, 2012-07-29 at 01:42 +0100, David Woodhouse wrote:
> >> If I don't hack it to switch the mux to IGD at boot time, I never manage
> >> to get a sane picture out of the Intel device after switching to it.
> >> It's late now, but I'll try to get a proper debug log of the working and
> >> failing cases tomorrow.
> >
> >  From the hacked kernel (after fixing vga_switcheroo_enable() not to do:
> > 		event.info = client->fb_info;
> >   		fb_notifier_call_chain(FB_EVENT_REMAP_ALL_CONSOLE, &event);
> > if client->fb_info is NULL)...
> >
> > http://david.woodhou.se/dmesg-boot-to-IGD (blank screen)
> > http://david.woodhou.se/dmesg-boot-to-IGD-and-switch-to-DIS (works)
> > http://david.woodhou.se/dmesg-boot-to-IGD-and-switch-to-DIS-and-back-to-IGD (works)
> >
> > Without switching to IGD at startup...
> >
> > http://david.woodhou.se/dmesg-boot-to-DIS (works)
> > http://david.woodhou.se/dmesg-boot-to-DIS-then-switch-to-IGD (blank)
> >
> 
> The general problem, at least for the case of booting to DIS and then 
> switching to IGD, is that the mode for the internal display isn't 
> correct, so it stays black.
> 
> It could get the right mode via DDC but this line is muxed as well. 
> 0x728 controls the DDC mux, writing 1 lets the IGD access it, 2 is the DIS.

So? We *switch* it before telling the IGD to enable its display (hotplug
the LVDS). So the DDC *should* be working, surely? Is it just that the
Intel driver is probing the LVDS once at boot when the panel isn't even
connected, and it should be made hotplug-capable?

The Radeon seems to cope... maybe. I note it doesn't actually come up in
1920x1200 with fbcon, although ISTR X was getting the right resolution.

> So what happens in dmesg-boot-to-DIS is that the intel card can't get 
> the mode via DDC and falls back to the garbage mode from VBT.
> Interestingly, there is a intel VBT on your MBP8,3, but it doesn't 
> contain the right modes. On my MBP6,2 there isn't a VBT at all and it 
> disables LVDS altogether if 0x728 isn't switched at boot.
> 
> Manually switching the mux is a bit messy, so I'm not too surprised that 
> it's blank in dmesg-boot-to-IGD.

That does actually work, if I disable the Radeon completely. With this
in early boot:
+       outb(1, 0x728);
+       outb(2, 0x710);
+       outb(2, 0x740);
+       outb(0, 0x750);
... the Intel framebuffer then comes up just fine on the internal
display. It *can't* drive external displays in that case (via the
standard Apple DP-VGA or DP-DVI adapters; I haven't tried real DP), but
the LVDS is fine.

> The gmux code you're using is a bit outdated, but if you use 
> git://kernel.ubuntu.com/sforshee/linux.git gmux-switcheroo and connect 
> an external display (I tested it with a DP one) you should be able to 
> boot to DIS and switch to the IGD and get output on the external display.
> 
> This leaves the problem of how to get i915 the right mode. Generally, 
> there are two options:
> 
> - Find a way so it gets the right mode when it initializes the LVDS. 
> This could be done by switching the DDC mux during lvds intialization. 
> See lock_ddc.patch for a crude prototype that works on my laptop if I'm 
> lucky and apple_gmux gets loaded before i915 and nouveau doesn't try to 
> use DDC at the same time.

Again, why is the LVDS initialisation happening when the LVDS isn't
connected anyway? Fix that, and your concerns become irrelevant. You
*can't* switch to IGD before apple_gmux is loaded, and the discrete card
shouldn't be poking it DDC when the panel has been hot-unplugged from it
either.

> Another way would be to get the right EDID without mux switching by 
> querying either the DIS driver or EFI (if you boot into the rEFIt shell 
> you can verify it's there, see http://andreas.meetr.de/efi/log/edid.txt, 
> to get it search for EdidDiscovered/EdidActive and dump it with dmem). 
> But to use this, we need a way to know which display this corresponds to 
> and I'm not sure how to do that.
> 
> - Make vga_switcheroo reprobe handle this. This would mean that we start 
> with a possibly broken mode and resize it once the mux get's switched 
> through vga_switcheroo. I'm not sure if thats a good idea.

"Possibly broken mode", in the case where there is no monitor attached
to the display. I think we can live with that. Surely it's the case for
an external monitor (which we also support) anyway?

In fact speaking of external monitors... it looks like it should be
possible to support using one graphics cards for the LVDS, and another
for the external DisplayPort. Perhaps they could be different seats of a
multi-seat system, with completely separate X servers, or maybe we'd do
it just to work around size/bandwidth limitations or for performance
reasons. Do we have any plan to allow that? We only switch both together
for now...

-- 
dwmw2

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