June 11, 2020 5:38 PM, "Ard Biesheuvel" <ard.biesheu...@arm.com> wrote:
> On 6/11/20 4:33 PM, greg@unrelenting.technology wrote: > >> June 11, 2020 5:17 PM, "Ard Biesheuvel" <ard.biesheu...@arm.com> wrote: >> On 6/11/20 4:07 PM, greg@unrelenting.technology wrote: >>> >> >> June 11, 2020 4:19 PM, "Ard Biesheuvel" <ard.biesheu...@arm.com> wrote: >> On 6/5/20 5:19 PM, Marcin Wojtas via groups.io wrote: >> Disabling ECAM shift is just a matter of exposing the iATU controls to the >> OS, right? Why do you >> need to disable it? >> >> I'm not sure what iATU controls are (and we don't want to do anything in the >> OS), >> but basically the current address is shifted by 0x8000 to only expose the >> last device to the OS, >> to work around the silicon bug (lack of some filtering thing) that causes >> devices to appear many >> many times. >> But actually most modern devices (e.g. AMD RX 480, Mellanox CX2) *do not* >> get duplicated at all, >> they show up >> in the first position, and this shift moves the memory way past that >> position and the OS sees >> no PCIe devices at all. The only device that was duplicated into all slots >> for me was a cheap SATA >> card. >> In my experience whether the device is duplicated seems to correlate with >> the "Legacy" field >> in the UEFI Shell's pci command. IIRC Marcin has explained the actual >> technical characteristic >> of these devices in some mail before. So it might actually be possible to >> decide whether to do the >> shift >> automatically at runtime depending on the inserted device (?) >> But a setting in the setup menu is easier to do and less magical. >> I've just been running with the shift reverted: >> https://github.com/myfreeweb/edk2-platforms/commit/36395be2a8707f6d396e07405eb9fe47b64cf964 >> to make my Radeon GPU work. >>> OK, the shift is definitely a hack, and your assertion that 'most modern >>> devices do not get >>> duplicated at all' does not match my experience, tbh. >>> Are these all devices that support ARI by any chance? >> >> Mellanox (ConnectX-2) and Intel (82599ES and good old 82576) NICs do. >> But AMD GPUs actually don't! Still the RX480 (POLARIS10) only works without >> the shift. > > Interesting. It all depends on whether the endpoint decodes the device field > to begin with: it > doesn't have to, since the root port at the other end should be doing the > filtering. > >> An older GPU (HD7970 I think) I've tried once was duplicated, but only >> literally duplicated (into >> two), >> not into *all* slots. > > This is because the iATU granule size is 64k, and so we are only exposing 64k > of ECAM space to the > CPU. (Other implementations of this IP that use smaller granule sizes don't > need this shift at all) > >>> The problem is that the PCIe IP is truly broken, and the lack of a root >>> port means that TLPs get >>> emitted that should never reach the device in the first place, and it is >>> not the job of the device >>> to filter these TLPs, or reason about their own device # in the first place. >> >> Well, it must be that AMD Radeons do reason about this :) >> and that sadly breaks the offset hack. > > This is interesting. I wouldn't expect the endpoint to have any awareness of > how the ECAM space is > exposed to the CPU. How does it fail exactly? As I said: it just doesn't get duplicated, so with the shift, the OS does not see it at all. I have no idea why exactly it doesn't get duplicated. -=-=-=-=-=-=-=-=-=-=-=- Groups.io Links: You receive all messages sent to this group. View/Reply Online (#61159): https://edk2.groups.io/g/devel/message/61159 Mute This Topic: https://groups.io/mt/74694919/21656 Group Owner: devel+ow...@edk2.groups.io Unsubscribe: https://edk2.groups.io/g/devel/unsub [arch...@mail-archive.com] -=-=-=-=-=-=-=-=-=-=-=-
