[Intel-gfx] [PATCH v2 17/19] drm/i915/dsb: Use DEwake to combat PkgC latency
Shankar, Uma
uma.shankar at intel.com
Wed Sep 13 18:08:42 UTC 2023
> -----Original Message-----
> From: Intel-gfx <intel-gfx-bounces at lists.freedesktop.org> On Behalf Of Ville
> Syrjala
> Sent: Wednesday, June 7, 2023 12:45 AM
> To: intel-gfx at lists.freedesktop.org
> Subject: [Intel-gfx] [PATCH v2 17/19] drm/i915/dsb: Use DEwake to combat PkgC
> latency
>
> From: Ville Syrjälä <ville.syrjala at linux.intel.com>
>
> Normally we could be in a deep PkgC state all the way up to the point when DSB
> starts its execution at the transcoders undelayed vblank. The DSB will then have
> to wait for the hardware to wake up before it can execute anything. This will
> waste a huge chunk of the vblank time just waiting, and risks the DSB execution
> spilling into the vertical active period. That will be very bad, especially when
> programming the LUTs as the anti-collision logic will cause DSB to corrupt LUT
> writes during vertical active.
>
> To avoid these problems we can instruct the DSB to pre-wake the display engined
> on a specific scanline so that everything will be 100% ready to go when we hit the
> transcoder's undelayed vblank.
>
> One annoyance is that the scanline is specified as just that, a single scanline. So if
> we happen to start the DSB execution after passing said scanline no DEwake will
> happen and we may drop back into some PkgC state before reaching the
> transcoder's undelayed vblank. To prevent that we'll use the "force DEwake" bit
> to manually force the display engined to stay awake. We'll then have to clear the
Nit: Typo in engine
> force bit again after the DSB is done (the force bit remains effective even when
> the DSB is otherwise disabled).
Approach looks good, this will help hardware be ready and maximize the chance of
update within the vblank.
> Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> ---
> drivers/gpu/drm/i915/display/intel_color.c | 2 +-
> drivers/gpu/drm/i915/display/intel_dsb.c | 91 +++++++++++++++++++---
> drivers/gpu/drm/i915/display/intel_dsb.h | 3 +-
> 3 files changed, 82 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_color.c
> b/drivers/gpu/drm/i915/display/intel_color.c
> index b3dd4013d058..c5a9ea53a718 100644
> --- a/drivers/gpu/drm/i915/display/intel_color.c
> +++ b/drivers/gpu/drm/i915/display/intel_color.c
> @@ -1824,7 +1824,7 @@ void intel_color_prepare_commit(struct
> intel_crtc_state *crtc_state)
> if (!crtc_state->pre_csc_lut && !crtc_state->post_csc_lut)
> return;
>
> - crtc_state->dsb = intel_dsb_prepare(crtc, 1024);
> + crtc_state->dsb = intel_dsb_prepare(crtc_state, 1024);
> if (!crtc_state->dsb)
> return;
>
> diff --git a/drivers/gpu/drm/i915/display/intel_dsb.c
> b/drivers/gpu/drm/i915/display/intel_dsb.c
> index 73d609507f24..3e32aa49b8eb 100644
> --- a/drivers/gpu/drm/i915/display/intel_dsb.c
> +++ b/drivers/gpu/drm/i915/display/intel_dsb.c
> @@ -7,11 +7,16 @@
> #include "gem/i915_gem_internal.h"
>
> #include "i915_drv.h"
> +#include "i915_irq.h"
> #include "i915_reg.h"
> +#include "intel_crtc.h"
> #include "intel_de.h"
> #include "intel_display_types.h"
> #include "intel_dsb.h"
> #include "intel_dsb_regs.h"
> +#include "intel_vblank.h"
> +#include "intel_vrr.h"
> +#include "skl_watermark.h"
>
> struct i915_vma;
>
> @@ -47,6 +52,8 @@ struct intel_dsb {
> * register.
> */
> unsigned int ins_start_offset;
> +
> + int dewake_scanline;
> };
>
> /**
> @@ -297,17 +304,40 @@ static void intel_dsb_align_tail(struct intel_dsb *dsb)
>
> void intel_dsb_finish(struct intel_dsb *dsb) {
> + struct intel_crtc *crtc = dsb->crtc;
> +
> + /*
> + * DSB_FORCE_DEWAKE remains active even after DSB is
> + * disabled, so make sure to clear it (if set during
> + * intel_dsb_commit()).
> + */
> + intel_dsb_reg_write_masked(dsb, DSB_PMCTRL_2(crtc->pipe, dsb->id),
> + DSB_FORCE_DEWAKE, 0);
We should also keep DSB_BLOCK_DEWAKE_EXTENSION set to 1, the default .
With this fixed or clarified, this is:
Reviewed-by: Uma Shankar <uma.shankar at intel.com>
> intel_dsb_align_tail(dsb);
> }
>
> -/**
> - * intel_dsb_commit() - Trigger workload execution of DSB.
> - * @dsb: DSB context
> - * @wait_for_vblank: wait for vblank before executing
> - *
> - * This function is used to do actual write to hardware using DSB.
> - */
> -void intel_dsb_commit(struct intel_dsb *dsb, bool wait_for_vblank)
> +static int intel_dsb_dewake_scanline(const struct intel_crtc_state
> +*crtc_state) {
> + struct drm_i915_private *i915 = to_i915(crtc_state->uapi.crtc->dev);
> + const struct drm_display_mode *adjusted_mode = &crtc_state-
> >hw.adjusted_mode;
> + unsigned int latency = skl_watermark_max_latency(i915);
> + int vblank_start;
> +
> + if (crtc_state->vrr.enable) {
> + vblank_start = intel_vrr_vmin_vblank_start(crtc_state);
> + } else {
> + vblank_start = adjusted_mode->crtc_vblank_start;
> +
> + if (adjusted_mode->flags & DRM_MODE_FLAG_INTERLACE)
> + vblank_start = DIV_ROUND_UP(vblank_start, 2);
> + }
> +
> + return max(0, vblank_start - intel_usecs_to_scanlines(adjusted_mode,
> +latency)); }
> +
> +static void _intel_dsb_commit(struct intel_dsb *dsb, u32 ctrl,
> + unsigned int dewake_scanline)
> {
> struct intel_crtc *crtc = dsb->crtc;
> struct drm_i915_private *dev_priv = to_i915(crtc->base.dev); @@ -
> 325,14 +355,49 @@ void intel_dsb_commit(struct intel_dsb *dsb, bool
> wait_for_vblank)
> }
>
> intel_de_write_fw(dev_priv, DSB_CTRL(pipe, dsb->id),
> - (wait_for_vblank ? DSB_WAIT_FOR_VBLANK : 0) |
> - DSB_ENABLE);
> + ctrl | DSB_ENABLE);
> +
> intel_de_write_fw(dev_priv, DSB_HEAD(pipe, dsb->id),
> i915_ggtt_offset(dsb->vma));
> +
> + if (dewake_scanline >= 0) {
> + int diff, hw_dewake_scanline;
> +
> + hw_dewake_scanline = intel_crtc_scanline_to_hw(crtc,
> +dewake_scanline);
> +
> + intel_de_write_fw(dev_priv, DSB_PMCTRL(pipe, dsb->id),
> + DSB_ENABLE_DEWAKE |
> +
> DSB_SCANLINE_FOR_DEWAKE(hw_dewake_scanline));
> +
> + /*
> + * Force DEwake immediately if we're already past
> + * or close to racing past the target scanline.
> + */
> + diff = dewake_scanline - intel_get_crtc_scanline(crtc);
> + intel_de_write_fw(dev_priv, DSB_PMCTRL_2(pipe, dsb->id),
> + (diff >= 0 && diff < 5 ? DSB_FORCE_DEWAKE :
> 0) |
> + DSB_BLOCK_DEWAKE_EXTENSION);
> + }
> +
> intel_de_write_fw(dev_priv, DSB_TAIL(pipe, dsb->id),
> i915_ggtt_offset(dsb->vma) + tail); }
>
> +/**
> + * intel_dsb_commit() - Trigger workload execution of DSB.
> + * @dsb: DSB context
> + * @wait_for_vblank: wait for vblank before executing
> + *
> + * This function is used to do actual write to hardware using DSB.
> + */
> +void intel_dsb_commit(struct intel_dsb *dsb,
> + bool wait_for_vblank)
> +{
> + _intel_dsb_commit(dsb,
> + wait_for_vblank ? DSB_WAIT_FOR_VBLANK : 0,
> + wait_for_vblank ? dsb->dewake_scanline : -1); }
> +
> void intel_dsb_wait(struct intel_dsb *dsb) {
> struct intel_crtc *crtc = dsb->crtc;
> @@ -363,7 +428,7 @@ void intel_dsb_wait(struct intel_dsb *dsb)
>
> /**
> * intel_dsb_prepare() - Allocate, pin and map the DSB command buffer.
> - * @crtc: the CRTC
> + * @crtc_state: the CRTC state
> * @max_cmds: number of commands we need to fit into command buffer
> *
> * This function prepare the command buffer which is used to store dsb @@ -
> 372,9 +437,10 @@ void intel_dsb_wait(struct intel_dsb *dsb)
> * Returns:
> * DSB context, NULL on failure
> */
> -struct intel_dsb *intel_dsb_prepare(struct intel_crtc *crtc,
> +struct intel_dsb *intel_dsb_prepare(const struct intel_crtc_state
> +*crtc_state,
> unsigned int max_cmds)
> {
> + struct intel_crtc *crtc = to_intel_crtc(crtc_state->uapi.crtc);
> struct drm_i915_private *i915 = to_i915(crtc->base.dev);
> struct drm_i915_gem_object *obj;
> intel_wakeref_t wakeref;
> @@ -420,6 +486,7 @@ struct intel_dsb *intel_dsb_prepare(struct intel_crtc
> *crtc,
> dsb->size = size / 4; /* in dwords */
> dsb->free_pos = 0;
> dsb->ins_start_offset = 0;
> + dsb->dewake_scanline = intel_dsb_dewake_scanline(crtc_state);
>
> return dsb;
>
> diff --git a/drivers/gpu/drm/i915/display/intel_dsb.h
> b/drivers/gpu/drm/i915/display/intel_dsb.h
> index 54e9e1dc31ee..16d80f434356 100644
> --- a/drivers/gpu/drm/i915/display/intel_dsb.h
> +++ b/drivers/gpu/drm/i915/display/intel_dsb.h
> @@ -11,9 +11,10 @@
> #include "i915_reg_defs.h"
>
> struct intel_crtc;
> +struct intel_crtc_state;
> struct intel_dsb;
>
> -struct intel_dsb *intel_dsb_prepare(struct intel_crtc *crtc,
> +struct intel_dsb *intel_dsb_prepare(const struct intel_crtc_state
> +*crtc_state,
> unsigned int max_cmds);
> void intel_dsb_finish(struct intel_dsb *dsb); void intel_dsb_cleanup(struct
> intel_dsb *dsb);
> --
> 2.39.3
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