Adding Rob back in CC, I don't know if he is subscribed to wayland-devel@. You forgot to CC dri-devel@ too. On Tue, 11 Feb 2020 17:18:52 -0500 Xiaowen Wu <wxiaowen@xxxxxxxxxxxxxx> wrote: > Hi Rob, > > If the vendor driver doesn't have the hwpipe sub-object and kms plane is > one-to-one mapped to hwpipe (sspp), > do you think if below approach is acceptable if we still want to > virtualize the kms plane to support 4K/8K scanout? > > 1. At kms atomic check before calling drm_atomic_helper_check, depending > on scanout width of plane A in state, add idle planes B (C,D,...) > into the same atomic state, backup and then modify > src_x/src_w/crtc_x/crtc_w of plane A and the affected planes B (C,D,...) > to meet scanout > width limits, and set crtc/fb of the affected planes B (C,D,...) same as > plane A. > > 2. At plane's state duplicate function, check if plane's > src_x/src_w/crtc_x/crtc_w are updated at step 1), if so revert the > change to > plane A's backup value to allow plane A's scanout to update again. These > value will again be updated in step 1) so nothing really changes > if plane A continues updating. > > 3. If plane A's scanout is updated or detached from crtc, detach > affected planes B (C,D,...) in the same atomic state in step 1) and then > run step 1) again. > > 4. If user want to commit plane B (C,D,...), the commit/test will fail > if planes are already used as sister plane of plane A. This failure is > same > as insufficient hwpipe from plane B (C,D,...). > > With above change, any downstream driver can support virtualized plane. > Also as the above approach is generic and not h/w specific, we can make > it a helper function and it's up to vendor to choose if they want to use > or not, if they don't have logic like drm/msm/disp/mdp5/mdp5_plane in > their downstream driver. > > Conceptional above changes didn't borrow hwpipe resources from other > plane but borrow planes themselves directly, however from user point of > view > they should not feel any difference. > > What do you think? > > BR, > Xiaowen Wu > > > On Tue Jan 21, 2020 at 4:12 PM Rob Clark <robdclark at gmail.com> wrote: > > On Fri, Jan 17, 2020 at 8:52 AM Matt Hoosier <matt.hoosier at > > gmail.com> wrote: > >> > >> Hi all, > >> > >> I'm confronting a situation where the hardware with which I work is > >> capable of driving connectors at 4K or 8K, but doing so requires > >> bonding the scanning of multiple planes together. > >> > >> The scenario is that you'd have a big primary framebuffer whose size > >> is too large for an individual hardware scanning pipeline on the > >> display controller to traverse within its maximum allowed clock rate. > >> > >> The hardware supplier's approach is to assign multiple planes, which > >> in the KMS driver map to hardware scanning pipelines, to each be > >> responsible for scanning a smaller section of the framebuffer. The > >> planes are all assigned to the same CRTC, and in concert with each > >> other they cover the whole area of the framebuffer and CRTC. > >> > >> This sounds a little bit wild to me. I hadn't been aware it's even > >> legal to have more than one plane treated a the source of scanout for > >> a single framebuffer. Maybe that distinction isn't really relevant > >> nowadays with universal plane support. > >> > > > > fwiw, have a look at drm/msm/disp/mdp5/mdp5_plane, which will allocate > > one or two hwpipe's from the devices global atomic state, depending on > > scanout width.. the hwpipe (sspp) is the physical resource behind a > > plane, so essentially the kms planes are virtualized. At some point > > if you have too many wide layers, the atomic test step will fail due > > to insufficient hwpipe's. But this sort of scenario is the reason for > > the test step. > > > > BR, > > -R > > > >> I'm wondering if anybody here knows whether this a legit approach for > >> a compositor's DRM backend to take? > >> > _______________________________________________ > wayland-devel mailing list > wayland-devel@xxxxxxxxxxxxxxxxxxxxx > https://lists.freedesktop.org/mailman/listinfo/wayland-devel
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