From mboxrd@z Thu Jan 1 00:00:00 1970 From: dhar@codeaurora.org Subject: Re: drm/msm/dpu: Correct dpu encoder spinlock initialization Date: Mon, 01 Jul 2019 15:59:13 +0530 Message-ID: References: <1561357632-15361-1-git-send-email-dhar@codeaurora.org> <627144af54459a203f1583d2ad9b390c@codeaurora.org> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <627144af54459a203f1583d2ad9b390c@codeaurora.org> Sender: linux-kernel-owner@vger.kernel.org To: Jeykumar Sankaran Cc: dri-devel@lists.freedesktop.org, linux-arm-msm@vger.kernel.org, freedreno@lists.freedesktop.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, robdclark@gmail.com, seanpaul@chromium.org, hoegsberg@chromium.org, abhinavk@codeaurora.org, chandanu@codeaurora.org, nganji@codeaurora.org, jshekhar@codeaurora.org List-Id: devicetree@vger.kernel.org On 2019-06-26 03:10, Jeykumar Sankaran wrote: > On 2019-06-24 22:44, dhar@codeaurora.org wrote: >> 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 >> > DP calls into set_encoder_mode during hotplug before even notifying the > u/s. Can you trace out the original caller of this stack? > > Even though the patch is harmless, I am not entirely convinced to move > this > initialization. Any call which acquires the lock before encoder_setup > will be a no-op since there will not be any physical encoder to work > with. > > Thanks and Regards, > Jeykumar S. > >>>> Change-Id: I5a18b95fa47397c834a266b22abf33a517b03a4e >>>> Signed-off-by: Shubhashree Dhar >>>> --- >>>> 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; In dpu_crtc_vblank(), we are looping through all the encoders in the present mode_config: https://github.com/torvalds/linux/blob/master/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c#L1082 and hence calling dpu_encoder_toggle_vblank_for_crtc() for all the encoders. But in dpu_encoder_toggle_vblank_for_crtc(), after acquiring the spinlock, we will do a early return for the encoders which are not currently assigned to our crtc: https://github.com/torvalds/linux/blob/master/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c#L1318. Since the encoder_setup for the secondary encoder(dp encoder in this case) is not called until dp hotplug, we are hitting kernel panic while acquiring the lock.