> On Fri, Jan 29, 2016 at 07:14:29PM -0500, Sinan Kaya wrote: >> On 1/29/2016 6:06 PM, Bjorn Helgaas wrote: >> > On Wed, Jan 20, 2016 at 11:13:04AM -0500, Sinan Kaya wrote: >> >> On 1/20/2016 11:04 AM, Lorenzo Pieralisi wrote: >> >>> >> >>> We want to get rid of PCI_PROBE_ONLY on ARM/ARM64: >> >> >> >> For platforms that does not have UEFI BIOS, it makes sense to remove >> the probe only >> >> option as the firmware is not doing anything. >> > >> > I don't understand this statement. It sounds like you mean "non-UEFI >> > BIOS firmware doesn't assign PCI BARs", but that's not true, so you >> > must mean something else. >> >> It depends on the firmware flavor. I know u-boot does some PCI >> assignment but it does minimum to use PCI itself not for OS >> consumption. It may not deal with with switches/bridges etc. or will >> only assign mem32 resources and not touch prefetchable. > > Ah, I see the problem. When you wrote "non-UEFI BIOS," I thought > "old-fashioned x86 BIOS," which generally do assign resources. But I > don't have much experience with other firmware like U-boot. There are > good reasons, e.g., portability and boot-time optimization, why > firmware might not touch things it doesn't need. That's especially > true for PCI resource assignment, where we know the OS must do it > itself anyway, and there's little point in doing it twice. > >> Most non-UEFI firmwares I have seen on ARM rely on device specific >> driver like synopsys etc. to do the device initialization and ask >> kernel to do the enumeration. >> >> ACPI systems on the other hand handle the resource assignment before >> the OS starts. > > My guess is that this is more of a tradition than anything actually > required by the spec. > > The bottom line is that Linux can't rely on much consistency across > the universe of architectures and firmwares. I think the only thing > that really makes sense for us to do is: > > - Read whatever assignments the firmware may have made > - Keep them unchanged if they seem sensible > - Reassign them if they aren't sensible > - Use quirks to handle exceptions > > Bjorn > +1 to this list. -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
