Re: drm/msm/dpu: Correct dpu encoder spinlock initialization

[dhar]

On 2019-06-25 03:56, Jeykumar Sankaran wrote:
> On 2019-06-23 23:27, Shubhashree Dhar wrote:
> > dpu encoder spinlock should be initialized during dpu encoder
> > init instead of dpu encoder setup which is part of commit.
> > There are chances that vblank control uses the uninitialized
> > spinlock if not initialized during encoder init.
> Not much can be done if someone is performing a vblank operation
> before encoder_setup is done.
> Can you point to the path where this lock is acquired before
> the encoder_setup?
>
> Thanks
> Jeykumar S.
> >

When running some dp usecase, we are hitting this callstack.

Process kworker/u16:8 (pid: 215, stack limit = 0x00000000df9dd930)
Call trace:
 spin_dump+0x84/0x8c
 spin_dump+0x0/0x8c
 do_raw_spin_lock+0x80/0xb0
 _raw_spin_lock_irqsave+0x34/0x44
 dpu_encoder_toggle_vblank_for_crtc+0x8c/0xe8
 dpu_crtc_vblank+0x168/0x1a0
 dpu_kms_enable_vblank+0[   11.648998]  vblank_ctrl_worker+0x3c/0x60
 process_one_work+0x16c/0x2d8
 worker_thread+0x1d8/0x2b0
 kthread+0x124/0x134

Looks like vblank is getting enabled earlier causing this issue and we 
are using the spinlock without initializing it.

Thanks,
Shubhashree

> > Change-Id: I5a18b95fa47397c834a266b22abf33a517b03a4e
> > Signed-off-by: Shubhashree Dhar <dhar@xxxxxxxxxxxxxx>
> > ---
> >  drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c | 3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
> > b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
> > index 5f085b5..22938c7 100644
> > --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
> > +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
> > @@ -2195,8 +2195,6 @@ int dpu_encoder_setup(struct drm_device *dev, 
> > struct
> > drm_encoder *enc,
> >  	if (ret)
> >  		goto fail;
> >
> > -	spin_lock_init(&dpu_enc->enc_spinlock);
> > -
> >  	atomic_set(&dpu_enc->frame_done_timeout, 0);
> >  	timer_setup(&dpu_enc->frame_done_timer,
> >  			dpu_encoder_frame_done_timeout, 0);
> > @@ -2250,6 +2248,7 @@ struct drm_encoder *dpu_encoder_init(struct
> > drm_device *dev,
> >
> >  	drm_encoder_helper_add(&dpu_enc->base, &dpu_encoder_helper_funcs);
> >
> > +	spin_lock_init(&dpu_enc->enc_spinlock);
> >  	dpu_enc->enabled = false;
> >
> >  	return &dpu_enc->base;