Re: [PATCH] PCI: Only enable IO window if supported

From: Bjorn Helgaas
Date: Thu Jun 18 2015 - 15:52:22 EST

On Thu, Jun 18, 2015 at 1:01 PM, Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
> On Thu, May 28, 2015 at 07:41:12AM -0500, Bjorn Helgaas wrote:
>> > > I'd like res->flags to reflect the capabilities of the hardware, not
>> > > whether the window is currently enabled.
>> > >
>> > Flag bits seem to be all taken. Could we use IORESOURCE_DISABLED for that
>> > purpose, or could that cause conflicts elsewhere ?
>> Yes, I think IORESOURCE_DISABLED would be appropriate for any I/O windows
>> below a host bridge that doesn't support I/O space.
> I integrated Lorenzo's patch and tried to get this working.
> Problem is that the use of a resource is widely checked with "!res->flags"
> throughout the code. That would have to be changed to something like
> "(!res->flags || (res->flags & IORESOURCE_DISABLED))" whereever it is used.
> I tried going with "!res->flags" instead, but have not been able to get it
> to work realiably; it is just very difficult to distinguish if "!res->flags"
> means that the resource has not yet been assigned or if it means that it is not
> supported.
> The correct approach, in my opinion, would be to go with IORESOURCE_DISABLED
> and make the necessary changes whereever needed. Effectively this means to
> replace the "!res->flags" check with something like pci_res_used() [ pick
> your preferred name ] and define it as
> #define pci_res_used(res) ((res)->flags && !((res)->flags & IORESOURCE_DISABLED))

I think that makes sense. Maybe "res_valid()"? It's not really
PCI-specific, and "used" is a little ambiguous. So is "valid", I

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