linux-kernel - Re: drm/msm/dpu: Correct dpu encoder spinlock initialization

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Date:   Tue, 25 Jun 2019 11:14:45 +0530
From:   dhar@...eaurora.org
To:     Jeykumar Sankaran <jsanka@...eaurora.org>
Cc:     dri-devel@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
        freedreno@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, robdclark@...il.com,
        seanpaul@...omium.org, hoegsberg@...omium.org,
        abhinavk@...eaurora.org, chandanu@...eaurora.org,
        nganji@...eaurora.org, jshekhar@...eaurora.org
Subject: Re: drm/msm/dpu: Correct dpu encoder spinlock initialization

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@...eaurora.org>
>> ---
>>  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;