On Thu, 2022-08-04 at 12:36 +0200, Lorenzo Pieralisi wrote: > On Tue, Aug 02, 2022 at 02:07:00PM +1000, Benjamin Herrenschmidt wrote: > > [...] > > > The case back then was that there existed some (how many ? there was > > one real example if I remember correctly) bogus firwmares that came out > > of UEFI with too small windows. We could just quirk those .... > > There is just one way to discover "how many" unfortunately, quirking > those can be more problematic than it seems. Yes it can be but I'm still keen to try, if anything to keep all UEFI+ACPI platforms on the same basic mechanism. > [...] > > > The alternative here would be to use ad-hock kludges for such system > > devices, to "register" the addresses early, and have some kind of hook > > in the PCI code that keeps track of them as they get remapped. > > That's what x86 does AFAICS (pcibios_save_fw_addr()), even though > it is used in a different scope (ie revert to FW address if the > resource allocation fails). Right. Another kludge... It won't work much better than IORESOURCE_PCI_FIXED the minute the device is below any amount of bridges that have themselves be re-assigned. Worst, we might have moved something else over to where the FW left that device. It's ugly as heck :-) Oh well... I also really don't like how it maintains that separate list, would be much nicer to have something hanging off pci_dev. ../... > > Opinions ? > > You may also want to look into IORESOURCE_PCI_FIXED even though the > last time I looked into I found some broken logic (basically the > immutable/"fixed" BAR resources should obviously take into account the > PCI tree hierarchy - upstream bridges, etc., which I don't think > IORESOURCE_PCI_FIXED does - how it works remains a bit of > a mystery for me). It doesn't really work for the reasons you cited ... or rather it works in limited cases. I did look into it as well ages ago, and unless things changed, it was broken and not easily fixable. Our resource allocation code is.... intricated. That leaves us with 3 overall routes I can think of (we can figure out the details next): 1) We can try to detect early those devices (easy with SPCR, are there more on aarch64 ? on x86 there is) and hammer them into place, flagging them somewhat and forcing them (and all their parents) to keep their resources. Pros: It's rather easy to implement, we can "register" the addresses early and have the PCI probe code match detected devices againt that list & flag them (for example IORESOURCE_PCI_FIXES :-) and their parents. Cons: It will force entire bus hierarchies to be fixed, which might not really help on firmwares that are known to setup sub-optimal apertures (or even completely b0rked ones). But we don't know who those are except maybe one or two if we dig down into the previous version of that discussion from a couple of years ago. 2) We can try to "keep track" of them as they move. Variant A. We do it the way efifb does it and wrap that in something a bit nicer as follow: - We add a helper to "record" a pci_dev/BAR#/offset combination and an other one to do the lookup & fixup of a FW originated address. - We make efifb quirk use that instead of its existing global "bar_resource". - We add a similar quirk to the ACPI code that parses SPCR and (maybe) another one for earlycon (hint they may be the same device, some deduplication would be useful). - We update 8250_pci (I assume pl01x are never PCI ?) to call this to "fixup" addresses obtained from earlycon. That's the easy bit. SPRC is trickier, we'd need to fixup addressed parsed from add_preferred_console() .. I'm not 100% sure there's a case where such an address would be added post-PCI-remap and we might incorrectly fix it up. I don't think so but ... Pros: It should (hopefully) not be overly complicated and reasonably self contained, low risk. Cons: - It's a bit more complicated than other solutions, though not insanely - This doesn't solve the problem of a driver such as earlycon being "live" accross the remapping (and thus means we'll probably still have verybose PCI probing with earlycon dying horribly). This is already partially broken since we temporarily disable decoding during probing but that's a small window ... We can look at solving that separately by adding on top of this registration mechanism: We *could* optionally register in our above helper a pair of callbacks that the PCI code would call for each registered "early device" before and after remapping to "suspend access" and "fixup address". Those would be ideally called around the remapping of the entire host bridge the device is on. 3) Keeping track, Variant B (note: the more I think about it, the more I prefer variant A but let's see what others think) We generalize pcibios_save_fw_addr() and for the sake of it, we move that into pci_dev which simplifies everything and gets rid of that separate list. Then, things like efifb, 8250_pci etc... do a lookup in there for addresses they obtain from screen_info, earlycon, add_preferred_console.. and on match, perform the necessary fixup. Assuming we are confident those addresses originate from before the PCI remapping that is. Pros: It *seems* even simpler than the above other options and maybe even faster. Cons: It's more resource intensive as we now backup original BARs for everything under the sun. It also doesn't provide a great path to address the case I mentioned earlier for dealing with "live" devices. That's all I came up with ... Any better ideas and any preferences ? At this point I'm reasonably keen on (2) (tracking variant A). I'll be travelling this weekend and next week, so probably won't have time to produce much code but this has been broken forever so I don't see a huge emergency. So unless somebody beats me to it or strongly objects, I'll start hacking at it in the next few weeks. Cheers, Ben.
