Re: [PATCH 02/26] drm/i915: don't stop+start FBC at every flip

Maarten Lankhorst
2015-10-29T12:05:40Z

Op 28-10-15 om 18:20 schreef Ville Syrjälä:
> On Wed, Oct 28, 2015 at 04:56:39PM +0000, Zanoni, Paulo R wrote:
>> Em Ter, 2015-10-27 às 20:32 +0200, Ville Syrjälä escreveu:
>>> On Tue, Oct 27, 2015 at 02:50:04PM -0200, Paulo Zanoni wrote:
>>>> The hardware already takes care of disabling and recompressing FBC
>>>> when we do a page flip, so all we need to do is to update the fence
>>>> registers and move on.
>>>>
>>>> One of the important things to notice is that on the pre-gen6
>>>> platforms the fence is programmed on the FBC control register and
>>>> the
>>>> documentation says we can't update the control register while FBC
>>>> is
>>>> enabled. This would basically mean we'd have to to disable+enable
>>>> FBC
>>>> at every flip in order to make sure the hardware tracking still
>>>> works,
>>>> which doesn't seem to make too much sense. So I sent an email to
>>>> the
>>>> hardware team requesting some clarification. The information I got
>>>> was
>>>> this:
>>>>
>>>> "I don't think any hardware is latching on to 0x100100, 0x100104,
>>>> or
>>>> the old fence number in FBC_CTL. Instructions against changing on
>>>> the
>>>> fly would be to simplify testing and ensure you don't miss any
>>>> invalidation that happened right at that time."
>>>>
>>>> So I guess we're fine for flips. But I can't really say I tested
>>>> FBC
>>>> on these ancient platforms - nor that I'll ever propose enabling
>>>> FBC
>>>> by default on them exactly because of problems like these.
>>> Yeah, I did this in my patches too, and IIRC it seemed to work just
>>> fine
>>> back then.
>>>
>>>> v2: Add comment at flush() (Chris).
>>>>
>>>> Testcase: igt/kms_frontbuffer_tracking/fbc*-fliptrack
>>>> Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
>>>> ---
>>>> drivers/gpu/drm/i915/i915_drv.h | 1 +
>>>> drivers/gpu/drm/i915/i915_reg.h | 3 +
>>>> drivers/gpu/drm/i915/intel_display.c | 1 -
>>>> drivers/gpu/drm/i915/intel_drv.h | 2 +
>>>> drivers/gpu/drm/i915/intel_fbc.c | 103
>>>> ++++++++++++++++++++++++++++++-
>>>> drivers/gpu/drm/i915/intel_frontbuffer.c | 1 +
>>>> 6 files changed, 108 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/i915/i915_drv.h
>>>> b/drivers/gpu/drm/i915/i915_drv.h
>>>> index ee14962..77da500 100644
>>>> --- a/drivers/gpu/drm/i915/i915_drv.h
>>>> +++ b/drivers/gpu/drm/i915/i915_drv.h
>>>> @@ -928,6 +928,7 @@ struct i915_fbc {
>>>> bool (*fbc_enabled)(struct drm_i915_private *dev_priv);
>>>> void (*enable_fbc)(struct intel_crtc *crtc);
>>>> void (*disable_fbc)(struct drm_i915_private *dev_priv);
>>>> + void (*flip_prepare)(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 8942532..3d598a2 100644
>>>> --- a/drivers/gpu/drm/i915/i915_reg.h
>>>> +++ b/drivers/gpu/drm/i915/i915_reg.h
>>>> @@ -2028,6 +2028,7 @@ enum skl_disp_power_wells {
>>>> #define FBC_CTL_C3_IDLE (1<<13)
>>>> #define FBC_CTL_STRIDE_SHIFT (5)
>>>> #define FBC_CTL_FENCENO_SHIFT (0)
>>>> +#define FBC_CTL_FENCENO_MASK 0xF
>>> It's only three bits on gen2. But bit 3 is MBZ and there are only 8
>>> fence registers on those platforms, so this is OK.
>>>
>>>> #define FBC_COMMAND 0x0320c
>>>> #define FBC_CMD_COMPRESS (1<<0)
>>>> #define FBC_STATUS 0x03210
>>>> @@ -2064,6 +2065,7 @@ enum skl_disp_power_wells {
>>>> #define DPFC_CTL_LIMIT_1X (0<<6)
>>>> #define DPFC_CTL_LIMIT_2X (1<<6)
>>>> #define DPFC_CTL_LIMIT_4X (2<<6)
>>>> +#define DPFC_CTL_FENCE_MASK 0xF
>>>> #define DPFC_RECOMP_CTL 0x320c
>>>> #define DPFC_RECOMP_STALL_EN (1<<27)
>>>> #define DPFC_RECOMP_STALL_WM_SHIFT (16)
>>>> @@ -2086,6 +2088,7 @@ enum skl_disp_power_wells {
>>>> #define FBC_CTL_FALSE_COLOR (1<<10)
>>>> /* The bit 28-8 is reserved */
>>>> #define DPFC_RESERVED (0x1FFFFF00)
>>>> +#define ILK_DPFC_FENCE_MASK 0xF
>>>> #define ILK_DPFC_RECOMP_CTL 0x4320c
>>>> #define ILK_DPFC_STATUS 0x43210
>>>> #define ILK_DPFC_FENCE_YOFF 0x43218
>>>> diff --git a/drivers/gpu/drm/i915/intel_display.c
>>>> b/drivers/gpu/drm/i915/intel_display.c
>>>> index bc1907e..d9378c3 100644
>>>> --- a/drivers/gpu/drm/i915/intel_display.c
>>>> +++ b/drivers/gpu/drm/i915/intel_display.c
>>>> @@ -11502,7 +11502,6 @@ static int intel_crtc_page_flip(struct
>>>> drm_crtc *crtc,
>>>> to_intel_plane(primary)-
>>>>> frontbuffer_bit);
>>>> mutex_unlock(&dev->struct_mutex);
>>>>
>>>> - intel_fbc_disable_crtc(intel_crtc);
>>>> intel_frontbuffer_flip_prepare(dev,
>>>> to_intel_plane(primary)-
>>>>> frontbuffer_bit);
>>>>
>>>> diff --git a/drivers/gpu/drm/i915/intel_drv.h
>>>> b/drivers/gpu/drm/i915/intel_drv.h
>>>> index 08847d0..9065a8f 100644
>>>> --- a/drivers/gpu/drm/i915/intel_drv.h
>>>> +++ b/drivers/gpu/drm/i915/intel_drv.h
>>>> @@ -1305,6 +1305,8 @@ void intel_fbc_invalidate(struct
>>>> drm_i915_private *dev_priv,
>>>> enum fb_op_origin origin);
>>>> void intel_fbc_flush(struct drm_i915_private *dev_priv,
>>>> unsigned int frontbuffer_bits, enum
>>>> fb_op_origin origin);
>>>> +void intel_fbc_flip_prepare(struct drm_i915_private *dev_priv,
>>>> + unsigned int frontbuffer_bits);
>>>> void intel_fbc_cleanup_cfb(struct drm_i915_private *dev_priv);
>>>>
>>>> /* intel_hdmi.c */
>>>> diff --git a/drivers/gpu/drm/i915/intel_fbc.c
>>>> b/drivers/gpu/drm/i915/intel_fbc.c
>>>> index d9d7e54..62f158b 100644
>>>> --- a/drivers/gpu/drm/i915/intel_fbc.c
>>>> +++ b/drivers/gpu/drm/i915/intel_fbc.c
>>>> @@ -82,6 +82,22 @@ static void i8xx_fbc_disable(struct
>>>> drm_i915_private *dev_priv)
>>>> DRM_DEBUG_KMS("disabled FBC\n");
>>>> }
>>>>
>>>> +static void i8xx_fbc_flip_prepare(struct drm_i915_private
>>>> *dev_priv)
>>>> +{
>>>> + struct intel_crtc *crtc = dev_priv->fbc.crtc;
>>>> + struct drm_framebuffer *fb = crtc->base.primary->fb;
>>>> + struct drm_i915_gem_object *obj = intel_fb_obj(fb);
>>>> + uint32_t val;
>>>> +
>>>> + /* Although the documentation suggests we can't change
>>>> DPFC_CONTROL
>>>> + * while compression is enabled, the hardware guys said
>>>> that updating
>>>> + * the fence register bits during a flip is fine. */
>>>> + val = I915_READ(FBC_CONTROL);
>>>> + val &= ~FBC_CTL_FENCENO_MASK;
>>>> + val |= obj->fence_reg;
>>>> + I915_WRITE(FBC_CONTROL, val);
>>>> +}
>>> IIRC I just called the enable function to reconstruct the entire
>>> register contents to avoid code duplication. But maybe that's not
>>> possible without reowrking the fbc state handling entirely
>>> (which I had done).
>>>> +
>>>> static void i8xx_fbc_enable(struct intel_crtc *crtc)
>>>> {
>>>> struct drm_i915_private *dev_priv = crtc->base.dev-
>>>>> dev_private;
>>>> @@ -161,6 +177,22 @@ static void g4x_fbc_enable(struct intel_crtc
>>>> *crtc)
>>>> DRM_DEBUG_KMS("enabled fbc on plane %c\n",
>>>> plane_name(crtc->plane));
>>>> }
>>>>
>>>> +static void g4x_fbc_flip_prepare(struct drm_i915_private
>>>> *dev_priv)
>>>> +{
>>>> + struct intel_crtc *crtc = dev_priv->fbc.crtc;
>>>> + struct drm_framebuffer *fb = crtc->base.primary->fb;
>>>> + struct drm_i915_gem_object *obj = intel_fb_obj(fb);
>>>> + uint32_t val;
>>>> +
>>>> + /* Although the documentation suggests we can't change
>>>> DPFC_CONTROL
>>>> + * while compression is enabled, the hardware guys said
>>>> that updating
>>>> + * the fence register bits during a flip is fine. */
>>>> + val = I915_READ(DPFC_CONTROL);
>>>> + val &= ~DPFC_CTL_FENCE_MASK;
>>>> + val |= obj->fence_reg;
>>>> + I915_WRITE(DPFC_CONTROL, val);
>>>> +}
>>>> +
>>>> static void g4x_fbc_disable(struct drm_i915_private *dev_priv)
>>>> {
>>>> u32 dpfc_ctl;
>>>> @@ -236,6 +268,31 @@ static void ilk_fbc_enable(struct intel_crtc
>>>> *crtc)
>>>> DRM_DEBUG_KMS("enabled fbc on plane %c\n",
>>>> plane_name(crtc->plane));
>>>> }
>>>>
>>>> +static void ilk_fbc_flip_prepare(struct drm_i915_private
>>>> *dev_priv)
>>>> +{
>>>> + struct intel_crtc *crtc = dev_priv->fbc.crtc;
>>>> + struct drm_framebuffer *fb = crtc->base.primary->fb;
>>>> + struct drm_i915_gem_object *obj = intel_fb_obj(fb);
>>>> + uint32_t val;
>>>> +
>>>> + /* Although the documentation suggests we can't change
>>>> DPFC_CONTROL
>>>> + * while compression is enabled, the hardware guys said
>>>> that updating
>>>> + * the fence register bits during a flip is fine. */
>>>> + val = I915_READ(ILK_DPFC_CONTROL);
>>>> + val &= ~ILK_DPFC_FENCE_MASK;
>>>> + val |= obj->fence_reg;
>>>> + I915_WRITE(ILK_DPFC_CONTROL, val);
>>>> +}
>>>> +
>>>> +static void snb_fbc_flip_prepare(struct drm_i915_private
>>>> *dev_priv)
>>>> +{
>>>> + struct intel_crtc *crtc = dev_priv->fbc.crtc;
>>>> + struct drm_framebuffer *fb = crtc->base.primary->fb;
>>>> + struct drm_i915_gem_object *obj = intel_fb_obj(fb);
>>>> +
>>>> + I915_WRITE(SNB_DPFC_CTL_SA, SNB_CPU_FENCE_ENABLE | obj-
>>>>> fence_reg);
>>>> +}
>>>> +
>>>> static void ilk_fbc_disable(struct drm_i915_private *dev_priv)
>>>> {
>>>> u32 dpfc_ctl;
>>>> @@ -1021,13 +1078,48 @@ void intel_fbc_flush(struct
>>>> drm_i915_private *dev_priv,
>>>> if (origin == ORIGIN_GTT)
>>>> return;
>>>>
>>>> + /* Hardware tracking already recompresses the CFB (nuke)
>>>> for us if FBC
>>>> + * is enabled and we do a page flip, so we can safely
>>>> ignore it here.
>>>> + * FBC may be disabled in case we got an invalidate()
>>>> before the
>>>> + * flush(), so we'll still have to check that case below.
>>>> */
>>>> + if (origin == ORIGIN_FLIP && dev_priv->fbc.enabled)
>>>> + return;
>>>> +
>>>> mutex_lock(&dev_priv->fbc.lock);
>>>>
>>>> dev_priv->fbc.busy_bits &= ~frontbuffer_bits;
>>>>
>>>> if (!dev_priv->fbc.busy_bits) {
>>>> - __intel_fbc_disable(dev_priv);
>>>> - __intel_fbc_update(dev_priv);
>>>> + if (origin == ORIGIN_FLIP) {
>>>> + __intel_fbc_update(dev_priv);
>>>> + } else {
>>>> + __intel_fbc_disable(dev_priv);
>>>> + __intel_fbc_update(dev_priv);
>>>> + }
>>>> + }
>>>> +
>>>> + mutex_unlock(&dev_priv->fbc.lock);
>>>> +}
>>>> +
>>>> +void intel_fbc_flip_prepare(struct drm_i915_private *dev_priv,
>>>> + unsigned int frontbuffer_bits)
>>>> +{
>>>> + unsigned int fbc_bits;
>>>> +
>>>> + if (!fbc_supported(dev_priv))
>>>> + return;
>>>> +
>>>> + mutex_lock(&dev_priv->fbc.lock);
>>>> +
>>>> + if (dev_priv->fbc.enabled) {
>>>> + fbc_bits = INTEL_FRONTBUFFER_PRIMARY(dev_priv-
>>>>> fbc.crtc->pipe);
>>> primary->frontbuffer_bit would seem better.
>> Why?
> Why not? It's there already stashed away for you to use. No need to
> sprinkle these INTEL_FRONTBUFFER... things all over the place.
>
>>>> + if (fbc_bits & frontbuffer_bits)
>>>> + dev_priv->fbc.flip_prepare(dev_priv);
>>> You would still have to disable+reenable if you need to eg.
>>> reallocate
>>> the compressed buffer, of if the new fb isn't suitable for fbc, or
>>> maybe
>>> if you need to change anything else in the control register.
>> Yes, but as far as I understand the frontbuffer tracking, this case
>> won't happen here. I'm assuming we'll always go through
>> intel_fbc_update() on these cases.
> Perhaps, but more by luck than by design. With the setplane and atomic
> APIs there's no difference between a page flip and other plane updates.
> So if you want to take advantage of the hw flip nuke, you would need to
> check how the plane state is going to change, and based on that decide
> whether a fence update is enough or disable+re-enable is needed. And in
> fact I don't see any fbc_disable before the flip, just an fbc_update
> after the fact. So seems to me the disable really should be in your
> flip_prepare hook in this case. And in fact the whole flip_prepare
> thing isn't even called from the setplane/atomic path.
I'm working on fixing that, but that still requires a few more patches until page_flip and atomic_commit are unified. :-)

If it's useful we could do a simple patch to do the same in atomic commit. I'm moving fb_bits to crtc_state anyway.

~Maarten