On Wed, Sep 21, 2016 at 02:10:55PM +0000, Gabriele Paoloni wrote:
Hi Bjorn
[...]
If future hardware is completely ECAM-compliant and we don't need any more MCFG quirks, that would be great.
But we'll still need to describe that memory-mapped config space somewhere. If that's done with PNP0C02 or similar devices (as is done on my x86 laptop), we'd be all set.
If we need to work around firmware in the field that doesn't do that, one possibility is a PNP quirk along the lines of quirk_amd_mmconfig_area().
So, if my understanding is correct, for platforms that have not been shipped yet you propose to use PNP0C02 in the ACPI table in order to declare a motherboard reserved resource whereas for shipped platforms you propose to have a quirk along pnp_fixups in order to track the resource usage even if values are hardcoded...correct?
Yes. I'm open to alternate proposals, but x86 uses PNP0C02, and following existing practice seems reasonable.
Before Tomasz came up with this patchset we had a call between the vendors involved in this PCI quirks saga and other guys from Linaro and ARM.
Lorenzo summarized the outcome as in the following link http://lkml.iu.edu/hypermail/linux/kernel/1606.2/03344.html
Since this quirks mechanism has been discussed for quite a long time now IMHO it would be good to have a last call including also you (Bjorn) so that we can all agree on what to do and we avoid changing our drivers again and again...
I think we're converging pretty fast. As far as I'm concerned, the v6 ECAM quirks implementation is perfect. The only remaining issue is reporting the ECAM resources, and I haven't seen objections to using PNP0C02 + PNP quirks for broken firmware.
There is the question of how or whether to associate a PNP0A03 PCI bridge with resources from a different PNP0C02 device, but that's not super important. If the hard-coded resources appear both in a quirk and in the PCI bridge driver, it's ugly but not the end of the world. We've still achieved the objective of avoiding landmines in the address space.
Bjorn