From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeykumar Sankaran Subject: Re: drm/msm/dpu: Correct dpu encoder spinlock initialization Date: Tue, 02 Jul 2019 11:21:20 -0700 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: Sender: linux-kernel-owner@vger.kernel.org To: dhar@codeaurora.org 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 2019-07-01 03:29, dhar@codeaurora.org wrote: > 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/dpu > 1/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/dpu > 1/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. This is the sequence in which the events are expected to happen: 1) DP connector is instantiated with an inactive state 2) Hot plug on DP 3) DP connector is activated 4) User space attaches a CRTC to the activated connector 5) CRTC is enabled 6) CRTC_VBLANK_ON is called 7) dpu_crtc_vblank is called. So can you help tracing out why dpu_crtc_vblank is called when the connector is not activated yet (no hotplug)? -- Jeykumar S