Subject: Re: [PATCH 1/7] drm/mediatek: fix atomic_state reference counting

From: Bibby Hsieh <[email-masked]>
Date: Thu, 28 Nov 2019 10:34:11 +0800

On Wed, 2019-11-27 at 17:56 +0800, Daniel Vetter wrote:
> On Wed, Nov 27, 2019 at 09:41:52AM +0800, Bibby Hsieh wrote:
> > On Tue, 2019-11-26 at 09:49 +0100, Daniel Vetter wrote:
> > > On Tue, Nov 26, 2019 at 02:29:26PM +0800, Bibby Hsieh wrote:
> > > > The DRM core takes care of all atomic state refcounting.
> > > > However, mediatek drm defers some work that accesses planes
> > > > and plane_states in drm_atomic_state, and must therefore
> > > > keep its own atomic state references until this work complete.
> > > >
> > > > We take the atomic_state reference in atomic_fulsh() and ensure all the
> > > > information in atomic_state already was updated in hardware for
> > > > showing on screen and then schedules unreference_work to drop references
> > > > on atomic_state.
> > > >
> > > > Fixes: 119f5173628a ("drm/mediatek: Add DRM Driver for Mediatek SoC MT8173.")
> > > >
> > > > Signed-off-by: Bibby Hsieh <[email-masked]>
> > >
> > > This looks strange. For one you implement your own reference counting - if
> > > drivers have a need for drm_atomic_state_put_irq then I
> > > think we should implement this in the core code.
> > >
> > > The other bit is that atomic commits are meant to simply wait for
> > > everything to finish - commit_tail doesn't hold locks, it's only ordered
> > > through drm_crtc_commit events (at least with the async implementation in
> > > the helpers), so you can just block there until your interrupt handler is
> > > done processing the commit. Depending how you want to do this you might
> > > want to wait before or after drm_atomic_helper_commit_hw_done().
> >
> > OK, I will try to add a simple wait/completion before
> > drm_atomic_helper_commit_hw_done() until the commit was processed.
> 
> Note that waiting before hw_done stalls the next commit. You only want to
> do that for e.g. irq handler that programs registers at vblank. If you
> have some cleanup work that runs after the new frame is already showing,
> you should wait for that _after_ hw_done, to avoid stalling the next flip.
> 
> Also if you stall after hw_done, you need to make either make sure you
> handle concurrency between multiple commits for that part yourself (since
> anything after hw_done isn't ordered anymore by the default helper stuff).
> -Daniel

Thanks for the friendly reminder. :P
Actually, this patch was created 2 years ago. We wanted to fix some
issue before. But I test it and do not see the issue we met before on my
platform after I remove this patch. I'm going to send all the patches
w/o "drm/mediatek: fix atomic_state reference counting" again today.

Bibby
> 
> >
> > Thanks.
> >
> > Bibby
> > > -Daniel
> > >
> > > > ---
> > > >  drivers/gpu/drm/mediatek/mtk_drm_crtc.c | 11 +++-
> > > >  drivers/gpu/drm/mediatek/mtk_drm_drv.c  | 79 +++++++++++++++++++++++++
> > > >  drivers/gpu/drm/mediatek/mtk_drm_drv.h  |  9 +++
> > > >  3 files changed, 97 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/drivers/gpu/drm/mediatek/mtk_drm_crtc.c b/drivers/gpu/drm/mediatek/mtk_drm_crtc.c
> > > > index 29d0582e90e9..68b92adc96bb 100644
> > > > --- a/drivers/gpu/drm/mediatek/mtk_drm_crtc.c
> > > > +++ b/drivers/gpu/drm/mediatek/mtk_drm_crtc.c
> > > > @@ -7,7 +7,7 @@
> > > >  #include <linux/pm_runtime.h>
> > > >
> > > >  #include <asm/barrier.h>
> > > > -
> > > > +#include <drm/drm_atomic.h>
> > > >  #include <drm/drm_atomic_helper.h>
> > > >  #include <drm/drm_plane_helper.h>
> > > >  #include <drm/drm_probe_helper.h>
> > > > @@ -47,6 +47,7 @@ struct mtk_drm_crtc {
> > > >  struct mtk_disp_mutex*mutex;
> > > >  unsigned intddp_comp_nr;
> > > >  struct mtk_ddp_comp**ddp_comp;
> > > > +struct drm_crtc_state*old_crtc_state;
> > > >  };
> > > >
> > > >  struct mtk_crtc_state {
> > > > @@ -362,6 +363,7 @@ static void mtk_crtc_ddp_hw_fini(struct mtk_drm_crtc *mtk_crtc)
> > > >  static void mtk_crtc_ddp_config(struct drm_crtc *crtc)
> > > >  {
> > > >  struct mtk_drm_crtc *mtk_crtc = to_mtk_crtc(crtc);
> > > > +struct drm_atomic_state *atomic_state = mtk_crtc->old_crtc_state->state;
> > > >  struct mtk_crtc_state *state = to_mtk_crtc_state(mtk_crtc->base.state);
> > > >  struct mtk_ddp_comp *comp = mtk_crtc->ddp_comp[0];
> > > >  unsigned int i;
> > > > @@ -399,6 +401,7 @@ static void mtk_crtc_ddp_config(struct drm_crtc *crtc)
> > > >  plane_state->pending.config = false;
> > > >  }
> > > >  mtk_crtc->pending_planes = false;
> > > > +mtk_atomic_state_put_queue(atomic_state);
> > > >  }
> > > >  }
> > > >
> > > > @@ -494,6 +497,7 @@ static void mtk_drm_crtc_atomic_begin(struct drm_crtc *crtc,
> > > >  static void mtk_drm_crtc_atomic_flush(struct drm_crtc *crtc,
> > > >        struct drm_crtc_state *old_crtc_state)
> > > >  {
> > > > +struct drm_atomic_state *old_atomic_state = old_crtc_state->state;
> > > >  struct mtk_drm_crtc *mtk_crtc = to_mtk_crtc(crtc);
> > > >  struct mtk_drm_private *priv = crtc->dev->dev_private;
> > > >  unsigned int pending_planes = 0;
> > > > @@ -512,8 +516,11 @@ static void mtk_drm_crtc_atomic_flush(struct drm_crtc *crtc,
> > > >  pending_planes |= BIT(i);
> > > >  }
> > > >  }
> > > > -if (pending_planes)
> > > > +if (pending_planes) {
> > > >  mtk_crtc->pending_planes = true;
> > > > +drm_atomic_state_get(old_atomic_state);
> > > > +mtk_crtc->old_crtc_state = old_crtc_state;
> > > > +}
> > > >  if (crtc->state->color_mgmt_changed)
> > > >  for (i = 0; i < mtk_crtc->ddp_comp_nr; i++)
> > > >  mtk_ddp_gamma_set(mtk_crtc->ddp_comp[i], crtc->state);
> > > > diff --git a/drivers/gpu/drm/mediatek/mtk_drm_drv.c b/drivers/gpu/drm/mediatek/mtk_drm_drv.c
> > > > index 6588dc6dd5e3..6c68283b6124 100644
> > > > --- a/drivers/gpu/drm/mediatek/mtk_drm_drv.c
> > > > +++ b/drivers/gpu/drm/mediatek/mtk_drm_drv.c
> > > > @@ -115,10 +115,85 @@ static int mtk_atomic_commit(struct drm_device *drm,
> > > >  return 0;
> > > >  }
> > > >
> > > > +struct mtk_atomic_state {
> > > > +struct drm_atomic_state base;
> > > > +struct list_head list;
> > > > +};
> > > > +
> > > > +static inline struct mtk_atomic_state *to_mtk_state(struct drm_atomic_state *s)
> > > > +{
> > > > +return container_of(s, struct mtk_atomic_state, base);
> > > > +}
> > > > +
> > > > +void mtk_atomic_state_put_queue(struct drm_atomic_state *state)
> > > > +{
> > > > +struct drm_device *drm = state->dev;
> > > > +struct mtk_drm_private *mtk_drm = drm->dev_private;
> > > > +struct mtk_atomic_state *mtk_state = to_mtk_state(state);
> > > > +unsigned long flags;
> > > > +
> > > > +spin_lock_irqsave(&mtk_drm->unreference.lock, flags);
> > > > +list_add_tail(&mtk_state->list, &mtk_drm->unreference.list);
> > > > +spin_unlock_irqrestore(&mtk_drm->unreference.lock, flags);
> > > > +
> > > > +schedule_work(&mtk_drm->unreference.work);
> > > > +}
> > > > +
> > > > +static void mtk_unreference_work(struct work_struct *work)
> > > > +{
> > > > +struct mtk_drm_private *mtk_drm = container_of(work,
> > > > +struct mtk_drm_private, unreference.work);
> > > > +unsigned long flags;
> > > > +struct mtk_atomic_state *state, *tmp;
> > > > +
> > > > +/*
> > > > + * framebuffers cannot be unreferenced in atomic context.
> > > > + * Therefore, only hold the spinlock when iterating unreference_list,
> > > > + * and drop it when doing the unreference.
> > > > + */
> > > > +spin_lock_irqsave(&mtk_drm->unreference.lock, flags);
> > > > +list_for_each_entry_safe(state, tmp, &mtk_drm->unreference.list, list) {
> > > > +list_del(&state->list);
> > > > +spin_unlock_irqrestore(&mtk_drm->unreference.lock, flags);
> > > > +drm_atomic_state_put(&state->base);
> > > > +spin_lock_irqsave(&mtk_drm->unreference.lock, flags);
> > > > +}
> > > > +spin_unlock_irqrestore(&mtk_drm->unreference.lock, flags);
> > > > +}
> > > > +
> > > > +static struct drm_atomic_state *
> > > > +mtk_drm_atomic_state_alloc(struct drm_device *dev)
> > > > +{
> > > > +struct mtk_atomic_state *mtk_state;
> > > > +
> > > > +mtk_state = kzalloc(sizeof(*mtk_state), GFP_KERNEL);
> > > > +if (!mtk_state)
> > > > +return NULL;
> > > > +
> > > > +if (drm_atomic_state_init(dev, &mtk_state->base) < 0) {
> > > > +kfree(mtk_state);
> > > > +return NULL;
> > > > +}
> > > > +
> > > > +INIT_LIST_HEAD(&mtk_state->list);
> > > > +
> > > > +return &mtk_state->base;
> > > > +}
> > > > +
> > > > +static void mtk_drm_atomic_state_free(struct drm_atomic_state *state)
> > > > +{
> > > > +struct mtk_atomic_state *mtk_state = to_mtk_state(state);
> > > > +
> > > > +drm_atomic_state_default_release(state);
> > > > +kfree(mtk_state);
> > > > +}
> > > > +
> > > >  static const struct drm_mode_config_funcs mtk_drm_mode_config_funcs = {
> > > >  .fb_create = mtk_drm_mode_fb_create,
> > > >  .atomic_check = drm_atomic_helper_check,
> > > >  .atomic_commit = mtk_atomic_commit,
> > > > +.atomic_state_alloc = mtk_drm_atomic_state_alloc,
> > > > +.atomic_state_free = mtk_drm_atomic_state_free
> > > >  };
> > > >
> > > >  static const enum mtk_ddp_comp_id mt2701_mtk_ddp_main[] = {
> > > > @@ -337,6 +412,10 @@ static int mtk_drm_kms_init(struct drm_device *drm)
> > > >  drm_kms_helper_poll_init(drm);
> > > >  drm_mode_config_reset(drm);
> > > >
> > > > +INIT_WORK(&private->unreference.work, mtk_unreference_work);
> > > > +INIT_LIST_HEAD(&private->unreference.list);
> > > > +spin_lock_init(&private->unreference.lock);
> > > > +
> > > >  return 0;
> > > >
> > > >  err_unset_dma_parms:
> > > > diff --git a/drivers/gpu/drm/mediatek/mtk_drm_drv.h b/drivers/gpu/drm/mediatek/mtk_drm_drv.h
> > > > index b6a82728d563..c37d835cf949 100644
> > > > --- a/drivers/gpu/drm/mediatek/mtk_drm_drv.h
> > > > +++ b/drivers/gpu/drm/mediatek/mtk_drm_drv.h
> > > > @@ -55,6 +55,13 @@ struct mtk_drm_private {
> > > >
> > > >  struct drm_atomic_state *suspend_state;
> > > >
> > > > +struct {
> > > > +struct work_structwork;
> > > > +struct list_headlist;
> > > > +/* lock for unreference list */
> > > > +spinlock_tlock;
> > > > +} unreference;
> > > > +
> > > >  bool dma_parms_allocated;
> > > >  };
> > > >
> > > > @@ -66,4 +73,6 @@ extern struct platform_driver mtk_dpi_driver;
> > > >  extern struct platform_driver mtk_dsi_driver;
> > > >  extern struct platform_driver mtk_mipi_tx_driver;
> > > >
> > > > +void mtk_atomic_state_put_queue(struct drm_atomic_state *state);
> > > > +
> > > >  #endif /* MTK_DRM_DRV_H */
> > > > --
> > > > 2.18.0
> > >
> >
> 
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch

_______________________________________________
linux-arm-kernel mailing list
[email-masked]
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel