Quoting Mika Kuoppala (2019-02-28 16:53:46)
> Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> writes:
>
> > Quoting Mika Kuoppala (2019-02-28 16:14:11)
> >> We have an exported function for stopping the engine before
> >> disabling a ringbuffer. Take it into use.
> >>
> >> v2: use fw on empty check
> >> v3: tail is tail
> >>
> >> Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> >> Signed-off-by: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx>
> >> Reviewed-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> >> ---
> >> drivers/gpu/drm/i915/intel_engine_cs.c | 3 ++
> >> drivers/gpu/drm/i915/intel_ringbuffer.c | 41 ++++++++++++++-----------
> >> 2 files changed, 26 insertions(+), 18 deletions(-)
> >>
> >> diff --git a/drivers/gpu/drm/i915/intel_engine_cs.c b/drivers/gpu/drm/i915/intel_engine_cs.c
> >> index df8f88142f1d..e35dc0386bf6 100644
> >> --- a/drivers/gpu/drm/i915/intel_engine_cs.c
> >> +++ b/drivers/gpu/drm/i915/intel_engine_cs.c
> >> @@ -856,6 +856,9 @@ void intel_engine_cancel_stop_cs(struct intel_engine_cs *engine)
> >> {
> >> struct drm_i915_private *dev_priv = engine->i915;
> >>
> >> + if (INTEL_GEN(dev_priv) < 3)
> >> + return;
> >> +
> >> GEM_TRACE("%s\n", engine->name);
> >>
> >> I915_WRITE_FW(RING_MI_MODE(engine->mmio_base),
> >> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
> >> index 1b96b0960adc..5fe28d9087b7 100644
> >> --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
> >> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
> >> @@ -604,26 +604,32 @@ static void ring_setup_status_page(struct intel_engine_cs *engine)
> >> flush_cs_tlb(engine);
> >> }
> >>
> >> +static bool ring_is_empty(struct intel_engine_cs *engine)
> >> +{
> >> + struct drm_i915_private *dev_priv = engine->i915;
> >> + const u32 base = engine->mmio_base;
> >> +
> >> + return (I915_READ_FW(RING_HEAD(base)) & HEAD_ADDR) ==
> >> + (I915_READ_FW(RING_TAIL(base)) & TAIL_ADDR);
> >> +}
> >> +
> >> static bool stop_ring(struct intel_engine_cs *engine)
> >> {
> >> struct drm_i915_private *dev_priv = engine->i915;
> >> + int ret;
> >>
> >> - if (INTEL_GEN(dev_priv) > 2) {
> >> - I915_WRITE_MODE(engine, _MASKED_BIT_ENABLE(STOP_RING));
> >> - if (intel_wait_for_register(dev_priv,
> >> - RING_MI_MODE(engine->mmio_base),
> >> - MODE_IDLE,
> >> - MODE_IDLE,
> >> - 1000)) {
> >> - DRM_ERROR("%s : timed out trying to stop ring\n",
> >> - engine->name);
> >> - /* Sometimes we observe that the idle flag is not
> >> - * set even though the ring is empty. So double
> >> - * check before giving up.
> >> - */
> >> - if (I915_READ_HEAD(engine) != I915_READ_TAIL(engine))
> >> - return false;
> >> - }
> >> + ret = intel_engine_stop_cs(engine);
> >> + if (ret == -ENODEV)
> >> + ret = 0;
> >> +
> >> + if (ret) {
> >> + /*
> >> + * Sometimes we observe that the idle flag is not
> >> + * set even though the ring is empty. So double
> >> + * check before giving up.
> >> + */
> >> + if (!ring_is_empty(engine))
> >> + return false;
> >
> > Hmm, thinking more about this, shouldn't we push this down to stop_cs()?
> >
> > If that's reporting an error in a situation where we can determine that
> > the ring is idle anyway, we can report the stop_cs succeeded.
>
> Makes sense, I will take a look.
>
> I felt small urge to deflate the 'stop'.
>
> Would it be confusing if we just did
> intel_engine_start|stop instead of stop_cs and
> cancel_stop_cs?
>
> So hmm:
>
> intel_engine_start()
> intel_engine_stop()
>
> these would only toggle the STOP_RING
>
> and for replacing stop_ring with:
> intel_engine_empty_ring()
intel_engine_clear_ring() / reset_ring(). Hmm, clear_ring of those two.
>
> for zeroing the heads.
>
> one 'stop' to rule the (ring)world!?
The counter argument is that _start() is a little too broad. The appeal
of stop_cs() is that it describing what it is doing, poking at the bit
to stop the CS advancing and nothing more. It frequently doesn't
succeed...
So I think it's not a worthy change, but I never did feel totally
satisfied with stop_cs -- cs is too short, but we do have usage with
xCS.
intel_engine_stop_command_streamer,
intel_engine_halt_command_streamer,
intel_engine_pause_command_streamer,
?
But intel_engine_clear_ring() I could be sold on.
-Chris
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