On Fri, Sep 08, 2023 at 08:56:53AM +0300, Ville Syrjälä wrote: > On Fri, Sep 08, 2023 at 12:51:09AM -0500, Lucas De Marchi wrote: > > On Fri, Sep 08, 2023 at 08:39:48AM +0300, Ville Syrjälä wrote: > > >On Thu, Sep 07, 2023 at 05:57:19PM -0700, Matt Roper wrote: > > >> On Thu, Sep 07, 2023 at 03:43:59PM -0500, Lucas De Marchi wrote: > > >> > On Thu, Sep 07, 2023 at 10:04:42AM -0700, Matt Roper wrote: > > >> > > On Thu, Sep 07, 2023 at 08:37:35AM -0700, Lucas De Marchi wrote: > > >> > > > From: Gustavo Sousa <gustavo.sousa@xxxxxxxxx> > > >> > > > > > >> > > > Xe2_LPD has sourth display on the same SOC. As such, define a new fake > > >> > > > > >> > > s/sourth/south/ > > >> > > > > >> > > You might also want to drop the word "same" from the description here > > >> > > since NDE and SDE are technically on different dies in this case (NDE is > > >> > > on the compute die, whereas SDE is on the SoC die). To be 100% accurate > > >> > > we'd want to identify SDE behavior via the PICA's GMD_ID (since PICA > > >> > > also lives on the SoC die for this platform). But since we've just been > > >> > > > >> > I'd not re-architect this based on where the PICA lives as it seems very > > >> > easy to change in future.... tying the SDE behavior to the PICA behavior > > >> > because they are on the same die, doesn't seem very future proof. > > >> > > >> The point is that tying it to any one thing for every platform is > > >> incorrect; figuring out a) which die is relevant to SDE behavior and b) > > >> how to fingerprint the variant and stepping of that die is very platform > > >> specific. Art specifically suggested using the PICA ID in cases where > > >> the PICA lives on the die that we need to fingerprint but the NDE does > > >> not. But again, that's not a silver bullet that can be used on every > > >> single platform. Nor is using the ISA bus ID like we've done for a long > > >> time. Nor is using the display version. Nor is using just the PCI ID. > > >> There's no single answer here, which is why we need a major rethink of > > >> our strategy at some point in the future. But that overhaul can wait > > >> for a future series; I just want to make sure that the commit messages > > >> here aren't causing further confusion. > > >> > > >> > > > >> > Here the real reason for the change is that from the SW perspective they > > >> > are under the same PCI device and there's no reason to look for a > > >> > different one. Maybe rewording it a "Xe2_LPD has south display on the > > >> > same PCI device" would be simpler? > > >> > > >> No, that would be even less correct; PCI device isn't really related to > > >> any of this. Obviously at the register level, everything our driver > > >> cares about (NDE, SDE, GT, etc.) is accessed through the same PCI device > > >> (e.g., 00:02.0 on an igpu). Under the hood the various pieces of that > > >> PCI device (NDE, SDE, render GT, media GT, etc.) might be located > > >> together on a single chip, or may be spread across different dies. When > > >> spread across different dies, those dies can be mixed-and-matched in > > >> various ways (and it seems like hardware design is trending toward more > > >> flexibility in mix-and-match). > > >> > > >> The register interface to the SDE (i.e., which registers exist and what > > >> bitfields they have inside) hasn't had any meaningful changes in a long > > >> time. And if it does change in the future, the _interface_ changes are > > >> probably more tied to the display IP version than to anything else. > > >> However there's some important SDE handling that the driver needs to do > > >> that may vary based on the identity of the specific die that's > > >> responsible for doing SDE I/O on a given platform. I.e., there may be > > >> I/O-related defects+workarounds that require special SDE programming > > >> when a certain die variant and/or stepping is present. There can also > > >> be differences in how lanes are physically wired up, resulting in pin > > >> mapping changes. In these cases we need to be able to fingerprint the > > >> identity of the specific die handling the I/O (which might be a compute > > >> die, an SoC die, and IOE die, a PCH die, etc.) and make our decisions > > >> accordingly. If the SDE I/O happens on the same die as the north > > >> display functionality, then using the display version might be an > > >> effective way to fingerprint. If the SDE I/O happens on a different die > > >> from the NDE, but on the same die the PICA lives on, the display > > >> architects suggested using the PICA ID in that case. If neither of > > >> those cases are true, then we may need to look at PCI IDs or something. > > >> > > >> In the past, the PCH was often where the SDE I/O responsibility was so > > >> we needed a way to identify exactly which PCH variant was present. The > > >> "PCH ID" that we try to match on during driver startup is entirely > > >> unrelated to the SDE; it's just a random bus that we know was always > > >> part of every PCH and always present in the same predictable PCI slot, > > >> so it's handy for identification purposes. The fact that we're still > > >> looking at the ISA bus on MTL today is 100% wrong because most (maybe > > >> all?) MTL platforms don't even have a PCH (so that ISA bus might be on a > > >> different die that we really don't care about at all). For MTL I > > >> believe the NDE and the SDE's I/O are both on the same SoC die, so we > > >> should really just be making our decisions based on IP version and/or > > >> graphics device ID. > > > > > >I think ideally SDE would have its own IP version/etc. we could > > >use to identify it. > > > > maybe some future platform > > > > > > > >I'm not really sure why we even started down this "fake PCH" route > > >since we never added that for BXT/GLK either, and they managed just > > > > it was originally done for the discrete cards, I think DG1, and got > > extended to the next ones. Differently than BXT/GLK it doesn't work > > at all to try finding the ISA bridge as that would end up matching the > > wrong one. > > BXT/GLK don't look for the ISA bridge either. Well, they do, but > they won't find a matching one and thus we're left with PCH_NONE. I guess we can also blame bspec for this mess a bit since for BXT/GLK it actually documents the SDE registers in the north display section, whereas everything else that has SDE registers documents them in the south display section. -- Ville Syrjälä Intel
