linux-kernel - Re: [PATCH 07/14] pci: don't shrink bridge resources

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Message-ID: <20100115133155.3bc1960c@jbarnes-piketon>
Date:	Fri, 15 Jan 2010 13:31:55 -0800
From:	Jesse Barnes <jbarnes@...tuousgeek.org>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ivan Kokshaysky <ink@...assic.park.msu.ru>,
	Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>,
	Alex Chiang <achiang@...com>,
	Bjorn Helgaas <bjorn.helgaas@...com>,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [PATCH 07/14] pci: don't shrink bridge resources

On Fri, 15 Jan 2010 13:09:31 -0800
Yinghai Lu <yinghai@...nel.org> wrote:

> On 01/15/2010 11:04 AM, Jesse Barnes wrote:
> > On Tue, 22 Dec 2009 15:02:27 -0800
> > Yinghai Lu <yinghai@...nel.org> wrote:
> > 
> >> when we are clearing leaf bridge resource and try to get big one,
> >> we could shrink the bridge if there is no resource under it.
> >>
> >> let check with old resource size and make sure we are trying to get
> >> big one.
> >>
> >> -v2: keep disable window print out, still could happen on non pci
> >> hotplug system
> >>
> >> Signed-off-by: Yinghai Lu <yinghai@...nel.org>
> >> ---
> >>  drivers/pci/setup-bus.c |   14 ++++++++++++--
> >>  1 files changed, 12 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
> >> index 9bb4435..d53b42e 100644
> >> --- a/drivers/pci/setup-bus.c
> >> +++ b/drivers/pci/setup-bus.c
> >> @@ -387,7 +387,7 @@ static void pbus_size_io(struct pci_bus *bus,
> >> resource_size_t min_size) {
> >>  	struct pci_dev *dev;
> >>  	struct resource *b_res = find_free_bus_resource(bus,
> >> IORESOURCE_IO);
> >> -	unsigned long size = 0, size1 = 0;
> >> +	unsigned long size = 0, size1 = 0, old_size;
> >>  
> >>  	if (!b_res)
> >>   		return;
> >> @@ -412,12 +412,17 @@ static void pbus_size_io(struct pci_bus *bus,
> >> resource_size_t min_size) }
> >>  	if (size < min_size)
> >>  		size = min_size;
> >> +	old_size = resource_size(b_res);
> >> +	if (old_size == 1)
> >> +		old_size = 0;
> > 
> > Do we even need these == 1 checks?  If old_size really was 1, it
> > means we had a very small decode range.  Might make more sense to
> > do...
> 
> when start=0 and end =0, will get old_size = 1

...
if (old_size == 1)
  old_size = 0
...
if (size < old_size)
  size = old_size
...


If old_size > 1 we'll make sure size doesn't decrease.

If old_size == 1, we'll never touch the changed size because size < 0
will never be true for size (unsigned).

However, if old_size == 1 and we left it at 1, we'd only set size =
old_size if size was 0, which is why I suggested the size check.

What am I missing?  When will size shrink?  I know it's just
nitpicking, I just want to make sure the code is clear, and that it's
obvious that we're preventing size from decreasing.

-- 
Jesse Barnes, Intel Open Source Technology Center
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