From mboxrd@z Thu Jan  1 00:00:00 1970
From: thomas.petazzoni@free-electrons.com (Thomas Petazzoni)
Date: Thu, 31 Jan 2013 16:47:35 +0100
Subject: [PATCH v2 19/27] pci: PCIe driver for Marvell Armada 370/XP
 systems
In-Reply-To: <20130131153625.GB23505@n2100.arm.linux.org.uk>
References: <20130130120344.GA29490@avionic-0098.mockup.avionic-design.de>
 <20130130150856.GJ23505@n2100.arm.linux.org.uk>
 <20130130151934.GK23505@n2100.arm.linux.org.uk>
 <20130130163659.75360dba@skate>
 <20130130154602.GL23505@n2100.arm.linux.org.uk>
 <20130131153041.35fa3b60@skate>
 <20130131145002.GZ23505@n2100.arm.linux.org.uk>
 <20130131155737.4ab97a0b@skate>
 <20130131150801.GA23505@n2100.arm.linux.org.uk>
 <20130131162237.79de29c4@skate>
 <20130131153625.GB23505@n2100.arm.linux.org.uk>
Message-ID: <20130131164735.3e1d4a88@skate>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

Dear Russell King - ARM Linux,

On Thu, 31 Jan 2013 15:36:25 +0000, Russell King - ARM Linux wrote:

> > The fixup is already specific to those bridges, since I am just setting
> > pci_sys_data->win_align_io to 64K for the particular buses that are
> > downstream the problematic bridges. So it doesn't affect any other bus
> > on the system, and therefore I don't think this fixup needs to be made
> > specific to a given vendor:device, no?
> 
> The pci_sys_data is not specific to one bus.  It's specific from the
> root bus downwards, and is shared by all child busses.

Ah, ok, that's the part I was missing.

> The problem is if you have some card or a conventional P2P bridge which
> has 4K windows.  If you merely set the alignment to 64K for all bridges,
> then all bridges get this treatment whether or not they need it.  That's
> what I'm trying to avoid.
> 
> Take, for instance, a cardbus bridge (remember, there are PCI cards which
> can be plugged in to give you a cardbus slot.)  I have a device here which
> can be plugged into a cardbus slot which has not just one P2P bridge but
> two, and a bunch of downsteam devices, including VGA, ethernet, USB, PS/2
> etc.  (Okay, Linux doesn't support this hardware because of crappy X86
> stuff, despite the fact Windows cope with it just fine.)
> 
> There have been cards in the past which have had P2P bridges on them as
> well.
> 
> So, simply believing that the only P2P bridges in the system will be
> those on the physical board is a mistake.

Yes, indeed, I understand this. I just thought this pci_sys_data
structure was per-bus. Of course, if it's shared by all buses on the
system, we need a way to apply this fixup only to the Marvell bridges.

Should I just hard-code this special fixup in
pcibios_window_alignment() with a check on VID/PID ?

Thanks,

Thomas
-- 
Thomas Petazzoni, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com