Re: [PATCH 01/18] drm/i915: Comments for semaphore clarification

From: Ben Widawsky <ben@bwidawsk.net>
To: Damien Lespiau <damien.lespiau@intel.com>
Cc: Intel-GFX <intel-gfx@lists.freedesktop.org>
Subject: Re: [PATCH 01/18] drm/i915: Comments for semaphore clarification
Date: Tue, 7 May 2013 10:00:53 -0700	[thread overview]
Message-ID: <20130507170053.GC28358@bwidawsk.net> (raw)
In-Reply-To: <20130507165116.GA28358@bwidawsk.net>

On Tue, May 07, 2013 at 09:51:16AM -0700, Ben Widawsky wrote:
> On Tue, May 07, 2013 at 02:54:06PM +0100, Damien Lespiau wrote:
> > On Sat, Apr 27, 2013 at 05:59:12PM -0700, Ben Widawsky wrote:
> > > Semaphores are tied very closely to the rings in the GPU. Trivial patch
> > > adds comments to the existing code so that when we add new rings we can
> > > include comments there as well. It also helps distinguish the ring to
> > > semaphore mailbox interactions by using the ringname in the semaphore
> > > data structures.
> > > 
> > > This patch should have no functional impact.
> > > 
> > > A subset of this patch was:
> > > Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
> > > Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
> > > ---
> > >  drivers/gpu/drm/i915/i915_reg.h         | 12 ++++++------
> > >  drivers/gpu/drm/i915/intel_ringbuffer.c | 18 +++++++++---------
> > >  drivers/gpu/drm/i915/intel_ringbuffer.h |  2 +-
> > >  3 files changed, 16 insertions(+), 16 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> > > index 4d66898..767aa32 100644
> > > --- a/drivers/gpu/drm/i915/i915_reg.h
> > > +++ b/drivers/gpu/drm/i915/i915_reg.h
> > > @@ -267,12 +267,12 @@
> > >  #define  MI_SEMAPHORE_UPDATE	    (1<<21)
> > >  #define  MI_SEMAPHORE_COMPARE	    (1<<20)
> > >  #define  MI_SEMAPHORE_REGISTER	    (1<<18)
> > > -#define  MI_SEMAPHORE_SYNC_RV	    (2<<16)
> > > -#define  MI_SEMAPHORE_SYNC_RB	    (0<<16)
> > > -#define  MI_SEMAPHORE_SYNC_VR	    (0<<16)
> > > -#define  MI_SEMAPHORE_SYNC_VB	    (2<<16)
> > > -#define  MI_SEMAPHORE_SYNC_BR	    (2<<16)
> > > -#define  MI_SEMAPHORE_SYNC_BV	    (0<<16)
> > > +#define  MI_SEMAPHORE_SYNC_RB	    (0<<16) /* RCS wait for BCS  (BRSYNC) */
> > > +#define  MI_SEMAPHORE_SYNC_RV	    (2<<16) /* RCS wait for VCS  (VRSYNC) */
> > > +#define  MI_SEMAPHORE_SYNC_VR	    (0<<16) /* VCS wait for RCS  (RVSYNC) */
> > > +#define  MI_SEMAPHORE_SYNC_VB	    (2<<16) /* VCS wait for BCS  (BVSYNC) */
> > > +#define  MI_SEMAPHORE_SYNC_BV	    (0<<16) /* BCS wait for VCS  (VBSYNC) */
> > > +#define  MI_SEMAPHORE_SYNC_BR	    (2<<16) /* BCS wait for RCS  (RBSYNC) */
> > 
> > Huum aren't the register names inverted in the comment? RCS waiting for
> > BCS would be RBSYNC? (Register read by RCS, written by BCS)
> > 
> > -- 
> > Damien
> 
> Admittedly this code is quite confusing. So I won't go past, I *think*
> The current comments are correct.
> 
> Using the example of the render waiting on the blitter:
> 
> gen6_ring_sync(render, blitter, seqno)
> iender emits a wait on:
> blitter->semaphore_register[RCS] (MI_SEMAPHORE_SYNC_BR)
> 
> gen6_add_request(blitter)
> update_mboxes(GEN6_RBSYNC)
> update_mboxes(GEN6_VBSYNC)
> 
> So in this case:
> MI_SEMAPHORE_SYNC_BR <==> GEN6_RBSYNC
> 
Okay, I've fixed this locally. Thanks for catching this.
To embarrass myself less, I got confused is the names are actually
correct, the string <FOO> wait for <BAR> is the part that's incorrect.

> 
> 
> > 
> > >  #define  MI_SEMAPHORE_SYNC_INVALID  (1<<0)
> > >  /*
> > >   * 3D instructions used by the kernel
> > > diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
> > > index 1d5d613..38751a7 100644
> > > --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
> > > +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
> > > @@ -1666,9 +1666,9 @@ int intel_init_render_ring_buffer(struct drm_device *dev)
> > >  		ring->get_seqno = gen6_ring_get_seqno;
> > >  		ring->set_seqno = ring_set_seqno;
> > >  		ring->sync_to = gen6_ring_sync;
> > > -		ring->semaphore_register[0] = MI_SEMAPHORE_SYNC_INVALID;
> > > -		ring->semaphore_register[1] = MI_SEMAPHORE_SYNC_RV;
> > > -		ring->semaphore_register[2] = MI_SEMAPHORE_SYNC_RB;
> > > +		ring->semaphore_register[RCS] = MI_SEMAPHORE_SYNC_INVALID;
> > > +		ring->semaphore_register[VCS] = MI_SEMAPHORE_SYNC_RV;
> > > +		ring->semaphore_register[BCS] = MI_SEMAPHORE_SYNC_RB;
> > >  		ring->signal_mbox[0] = GEN6_VRSYNC;
> > >  		ring->signal_mbox[1] = GEN6_BRSYNC;
> > >  	} else if (IS_GEN5(dev)) {
> > > @@ -1825,9 +1825,9 @@ int intel_init_bsd_ring_buffer(struct drm_device *dev)
> > >  		ring->irq_put = gen6_ring_put_irq;
> > >  		ring->dispatch_execbuffer = gen6_ring_dispatch_execbuffer;
> > >  		ring->sync_to = gen6_ring_sync;
> > > -		ring->semaphore_register[0] = MI_SEMAPHORE_SYNC_VR;
> > > -		ring->semaphore_register[1] = MI_SEMAPHORE_SYNC_INVALID;
> > > -		ring->semaphore_register[2] = MI_SEMAPHORE_SYNC_VB;
> > > +		ring->semaphore_register[RCS] = MI_SEMAPHORE_SYNC_VR;
> > > +		ring->semaphore_register[VCS] = MI_SEMAPHORE_SYNC_INVALID;
> > > +		ring->semaphore_register[BCS] = MI_SEMAPHORE_SYNC_VB;
> > >  		ring->signal_mbox[0] = GEN6_RVSYNC;
> > >  		ring->signal_mbox[1] = GEN6_BVSYNC;
> > >  	} else {
> > > @@ -1871,9 +1871,9 @@ int intel_init_blt_ring_buffer(struct drm_device *dev)
> > >  	ring->irq_put = gen6_ring_put_irq;
> > >  	ring->dispatch_execbuffer = gen6_ring_dispatch_execbuffer;
> > >  	ring->sync_to = gen6_ring_sync;
> > > -	ring->semaphore_register[0] = MI_SEMAPHORE_SYNC_BR;
> > > -	ring->semaphore_register[1] = MI_SEMAPHORE_SYNC_BV;
> > > -	ring->semaphore_register[2] = MI_SEMAPHORE_SYNC_INVALID;
> > > +	ring->semaphore_register[RCS] = MI_SEMAPHORE_SYNC_BR;
> > > +	ring->semaphore_register[VCS] = MI_SEMAPHORE_SYNC_BV;
> > > +	ring->semaphore_register[BCS] = MI_SEMAPHORE_SYNC_INVALID;
> > >  	ring->signal_mbox[0] = GEN6_RBSYNC;
> > >  	ring->signal_mbox[1] = GEN6_VBSYNC;
> > >  	ring->init = init_ring_common;
> > > diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
> > > index d66208c..785df13 100644
> > > --- a/drivers/gpu/drm/i915/intel_ringbuffer.h
> > > +++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
> > > @@ -102,7 +102,7 @@ struct  intel_ring_buffer {
> > >  				   struct intel_ring_buffer *to,
> > >  				   u32 seqno);
> > >  
> > > -	u32		semaphore_register[3]; /*our mbox written by others */
> > > +	u32		semaphore_register[I915_NUM_RINGS]; /*our mbox written by others */
> > >  	u32		signal_mbox[2]; /* mboxes this ring signals to */
> > >  	/**
> > >  	 * List of objects currently involved in rendering from the
> > > -- 
> > > 1.8.2.1
> > > 
> > > _______________________________________________
> > > Intel-gfx mailing list
> > > Intel-gfx@lists.freedesktop.org
> > > http://lists.freedesktop.org/mailman/listinfo/intel-gfx
> 
> -- 
> Ben Widawsky, Intel Open Source Technology Center
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> Intel-gfx mailing list
> Intel-gfx@lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/intel-gfx

-- 
Ben Widawsky, Intel Open Source Technology Center