linux-kernel - Re: [BUG] 2.6.26-rc1 broke X on SPARC Ultra5

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Date:	Wed, 4 Jun 2008 10:06:34 +0200
From:	Mikael Pettersson <mikpe@...uu.se>
To:	David Miller <davem@...emloft.net>
Cc:	airlied@...il.com, mikpe@...uu.se, sparclinux@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [BUG] 2.6.26-rc1 broke X on SPARC Ultra5

David Miller writes:
 > From: "Dave Airlie" <airlied@...il.com>
 > Date: Wed, 4 Jun 2008 06:45:57 +1000
 > 
 > > Wow thats a major userspace regression to ship, we'd never get away
 > > with doing that on x86 platforms.
 > 
 > x86 has how many maintainers and contributors last time you checked?
 > 
 > Meanwhile X itself shipped mostly-non-working for PCI devices on sparc
 > for years.  And would you also not argue that it's broken to begin
 > with that the older X servers cannot work properly without a root PCI
 > controller being there?
 > 
 > The only way I can work around this issue is to provide a virtual host
 > bridge driver in the kernel, and I tried to do that, but it doesn't
 > work which is why the change got installed that did.
 > 
 > We'd need this because on many sparc64 machines the PCI host bridge
 > (and some sub-bridges) aren't even accessible via PCI config space.
 > 
 > If you provide a virtual host bridge, you have to emulate all of
 > the PCI config space accesses, you have to provide the expected
 > linkage and hierarchy with the rest of the PCI devices, and you
 > also have to do all of the I/O and MEM space range bits correctly
 > too.
 > 
 > For PCI-E and sub-bridges this becomes even more complicated, and
 > frankly a waste of time.
 > 
 > In short you have to implement an entire non-trivial emulation layer
 > for this stuff.
 > 
 > I'm the only sparc64 platform developer, so my time is better spent
 > moving forward and making sure that libpciaccess based X servers
 > aren't so broken and do the right thing in a way which works in a
 > maintainable long term manner.

Indeed. You need to prioritize, and FWIW I support your decision.

/Mikael
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