linux-kernel - Re: [PATCH] PCI: Always set prefetchable base/limit upper32 registers

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Date:	Mon, 30 Nov 2009 16:53:44 -0700
From:	Alex Williamson <alex.williamson@...com>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	jbarnes@...tuousgeek.org, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PCI: Always set prefetchable base/limit upper32
 registers

On Mon, 2009-11-30 at 15:32 -0800, Yinghai Lu wrote:
> Alex Williamson wrote:
> > On Mon, 2009-11-30 at 14:12 -0800, Yinghai Lu wrote:
> >> Alex Williamson wrote: 
> >>> I don't believe the PCI spec dictates whether the upper 32bit base
> >>> should be 0 or -1, so it's purely a BIOS initialization choice and Linux
> >>> should properly handle both.  If the hardware only supports 32bit
> >>> prefetchable windows, the hardware will drop the write, just as it did
> >>> for every 2.6 kernel before 1f82de10.  Thanks,
> >> current code:
> >>
> >> #define  PCI_PREF_RANGE_TYPE_MASK 0x0fUL
> >> #define  PCI_PREF_RANGE_TYPE_32 0x00     
> >> #define  PCI_PREF_RANGE_TYPE_64 0x01
> >> #define  PCI_PREF_RANGE_MASK    (~0x0fUL)
> >>
> >> if the HW state the pref mmio is 64bit, we will touch upper 32bit. otherwise we will not touch it.
> > 
> > Really, where?  Please paste the code that writes to
> > PCI_PREF_BASE_UPPER32 in the case of hardware supporting a 64bit
> > prefetchable window.  I only see this happening if we are assigning it
> > to an IORESOURCE_MEM_64 resources.
> 
> IORESOURCE_MEM_64 get set when PCI_PREF_RANGE_TYPE_64 is set.
> 
> in probe.c::pci_read_bridge_bases()

Ah, I think I see where you're going.  We only set IORESOURCE_MEM_64 if
base <= limit, ie. the BIOS has programmed the prefetchable range.  This
is not a requirement by the PCI spec.  In my case the BIOS has left base
> limit, just as Linux would do if it disabled the range, so we never
set this flag.

> setup-bus.c::pci_bridge_check_ranges()

This is only checking that the upper 32bits is actually implemented,
should we have already set the IORESOURCE_MEM_64 from the function
above, which we haven't.  

So, in my case I have a 64bit capable prefetchable range, that the BIOS
has not programmed and is not required to program.  We assign it to a
32bit window, and never touch the UPPER32 registers.

Alex

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