On Mon, 2023-08-28 at 17:16 -0700, Matt Roper wrote:
> On Mon, Aug 28, 2023 at 09:20:34AM +0300, Vinod Govindapillai wrote:
> > In LNL onwards, FBC can be associated to the first three planes.
>
> The title of this patch shouldn't say "any plane" when the reality is
> that only the first three support FBC (the upper two do not).
>
> > The FBC will be enabled for first FBC capable visible plane
> > until the userspace can select one of these FBC capable plane
> > explicitly
>
> Even if we add new Intel-specific uapi to select this explicitly, is any
> userspace actually going to use it? Would it make more sense to try to
> come up with a heuristic to guess which plane would benefit the most and
> switch to that automatically without userspace needing to be involved in
> the decision? For that matter, do we have a real-world use case lined
> up where we can see that switching FBC to a higher plane is beneficial?
> Even if the hardware suddenly has this capability, it isn't necessarily
> worth adding the extra complexity to the driver if we don't expect to
> get real-world benefit from it.
>
> BTW, I'm not super familiar with all the FBC-specific details, but it
> feels like if we do go forward with this, the decision to select a
> specific plane for FBC usage should be handled more deliberately during
> the atomic check phase. Right now it doesn't seem like we're really
> making a firm decision on which plane to use, and we're probably not
> handling all the cases where the register needs to be reprogrammed
> if/when the FBC moves from one plane to another (potentially on a
> per-frame basis).
Hi Matt,
Agree with the comments about the subject line and also about your suggestions about some code
changes, will update accordingly.
Yes.. the logic for how to choose a plane for FBC is still open.
While discussing with Uma, it was decided that we split this task into two where we first have this
possibility to associate FBC to first three planes and then decide on this logic to select the plane
for fbc after discussing with Ville. ( Jira VLK-19372 / VLK-21508)
In this patch, "fbc" pointer is associated with first three plane implying those three are FBC
capable. And because there is no selection logic there, I choose the first available fbc capable
plane for FBC and the rest two to have a no_fbc_reason as "fbc enabled on another plane" which will
prevent them from being configured for FBC.
Ville has done refactoring to FBC code earlier and I think the current code flow should handle
disable/enable/register handling etc. Ville had some comments about the approach I explained above,
I have asked for some clarifications
BR
Vinod
>
> >
> > Bspec: 69560
> > Signed-off-by: Vinod Govindapillai <vinod.govindapillai@xxxxxxxxx>
> > ---
> > drivers/gpu/drm/i915/display/intel_fbc.c | 29 +++++++++++++++++++
> > .../drm/i915/display/skl_universal_plane.c | 5 +++-
> > drivers/gpu/drm/i915/i915_reg.h | 4 +++
> > 3 files changed, 37 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/i915/display/intel_fbc.c b/drivers/gpu/drm/i915/display/intel_fbc.c
> > index 45e205a0f740..62f59630d410 100644
> > --- a/drivers/gpu/drm/i915/display/intel_fbc.c
> > +++ b/drivers/gpu/drm/i915/display/intel_fbc.c
> > @@ -649,6 +649,21 @@ static void skl_fbc_program_cfb_stride(struct intel_fbc *fbc)
> > CHICKEN_FBC_STRIDE_MASK, val);
> > }
> >
> > +static u32 lnl_plane_binding(struct intel_fbc *fbc)
> > +{
> > + switch (fbc->state.plane->id) {
> > + default:
> > + MISSING_CASE(fbc->state.plane->id);
> > + fallthrough;
> > + case 0:
> > + return DPFC_CTL_PLANE_BINDING_1;
> > + case 1:
> > + return DPFC_CTL_PLANE_BINDING_2;
> > + case 2:
> > + return DPFC_CTL_PLANE_BINDING_3;
> > + }
> > +}
> > +
> > static u32 ivb_dpfc_ctl(struct intel_fbc *fbc)
> > {
> > const struct intel_fbc_state *fbc_state = &fbc->state;
> > @@ -660,6 +675,9 @@ static u32 ivb_dpfc_ctl(struct intel_fbc *fbc)
> > if (IS_IVYBRIDGE(i915))
> > dpfc_ctl |= DPFC_CTL_PLANE_IVB(fbc_state->plane->i9xx_plane);
> >
> > + if (DISPLAY_VER(i915) >= 20)
> > + dpfc_ctl |= lnl_plane_binding(fbc);
> > +
> > if (fbc_state->fence_id >= 0)
> > dpfc_ctl |= DPFC_CTL_FENCE_EN_IVB;
> >
> > @@ -1250,6 +1268,17 @@ static int intel_fbc_check_plane(struct intel_atomic_state *state,
> > }
> > }
> >
> > + /*
> > + * From LNL, FBC can be assigned on any plane. Until a provision is
> > + * provided for the userspace to select a plane for FBC, lets select
> > + * the first visible plane that is FBC capable.
> > + */
> > + if (DISPLAY_VER(i915) >= 20 && fbc->state.plane &&
>
> Isn't the fbc->state.plane here redundant with the plane check on the
> next line (since a NULL plane wouldn't match there either)?
>
> > + fbc->state.plane != plane) {
> > + plane_state->no_fbc_reason = "fbc enabled on another plane";
>
> If you set this here...
>
> > + return 0;
> > + }
> > +
> > plane_state->no_fbc_reason = NULL;
> >
> > return 0;
> > diff --git a/drivers/gpu/drm/i915/display/skl_universal_plane.c
> > b/drivers/gpu/drm/i915/display/skl_universal_plane.c
> > index 4d01c7ae4485..1291351c9941 100644
> > --- a/drivers/gpu/drm/i915/display/skl_universal_plane.c
> > +++ b/drivers/gpu/drm/i915/display/skl_universal_plane.c
> > @@ -1962,7 +1962,10 @@ static bool skl_plane_has_fbc(struct drm_i915_private *dev_priv,
> > if ((DISPLAY_RUNTIME_INFO(dev_priv)->fbc_mask & BIT(fbc_id)) == 0)
> > return false;
> >
> > - return plane_id == PLANE_PRIMARY;
> > + if (DISPLAY_VER(dev_priv) >= 20)
> > + return plane_id <= PLANE_SPRITE1;
> > + else
> > + return plane_id == PLANE_PRIMARY;
>
> ...and also point all three FBC-capable planes at the pipe's FBC
> structure, then won't intel_fbc_update() see the non-NULL reason and try
> to turn off the pipe's FBC (even though it's being used on a different
> plane)?
>
>
> Matt
>
> > }
> >
> > static struct intel_fbc *skl_plane_fbc(struct drm_i915_private *dev_priv,
> > diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> > index aefad14ab27a..b207774f3c33 100644
> > --- a/drivers/gpu/drm/i915/i915_reg.h
> > +++ b/drivers/gpu/drm/i915/i915_reg.h
> > @@ -1327,6 +1327,10 @@
> > #define DPFC_CTL_PLANE_IVB(i9xx_plane) REG_FIELD_PREP(DPFC_CTL_PLANE_MASK_IVB,
> > (i9xx_plane))
> > #define DPFC_CTL_FENCE_EN_IVB REG_BIT(28) /* ivb+ */
> > #define DPFC_CTL_PERSISTENT_MODE REG_BIT(25) /* g4x-snb */
> > +#define DPFC_CTL_PLANE_BINDING_MASK REG_GENMASK(12, 11) /* XE */
> > +#define DPFC_CTL_PLANE_BINDING_1 REG_FIELD_PREP(DPFC_CTL_PLANE_BINDING_MASK, 0)
> > /* XE */
> > +#define DPFC_CTL_PLANE_BINDING_2 REG_FIELD_PREP(DPFC_CTL_PLANE_BINDING_MASK, 1)
> > /* XE */
> > +#define DPFC_CTL_PLANE_BINDING_3 REG_FIELD_PREP(DPFC_CTL_PLANE_BINDING_MASK, 2)
> > /* XE */
> > #define DPFC_CTL_FALSE_COLOR REG_BIT(10) /* ivb+ */
> > #define DPFC_CTL_SR_EN REG_BIT(10) /* g4x only */
> > #define DPFC_CTL_SR_EXIT_DIS REG_BIT(9) /* g4x only */
> > --
> > 2.34.1
> >
>
