On Fri, Jul 11, 2014 at 11:40 AM, Bjorn Helgaas <bhelgaas@google.com> wrote:
> On Fri, Jul 11, 2014 at 12:21 PM, Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
>> On Fri, Jul 11, 2014 at 11:09 AM, Yinghai Lu <yinghai@kernel.org> wrote:
>>>
>>> If the BAR have all 0, cpu can not access it as hw will forward access to ram
>>> controller according to routing table.
>>
>> On PC's, yes (also likely with many devices - there are definitely
>> devices out there were setting the BAR to zero disables it).
>
> Ooh, we might trip over this some day on a platform with host bridge
> address translation that maps to PCI bus address 0.  I don't think we
> have anything in the allocator that avoids bus address 0 in that case.

Anyway, I draft RFC one that replace flags = 0 with flags |=
IORESOURCE_UNSET | IORESOURCE_DISABLEd.

Let's see how many drivers will fail.

Yinghai