Re: [PATCH] drm: zynqmp_dpsub: Always register bridge

From: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
To: Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
	Sean Anderson <sean.anderson@linux.dev>
Cc: linux-arm-kernel@lists.infradead.org,
	Michal Simek <michal.simek@amd.com>,
	linux-kernel@vger.kernel.org, Daniel Vetter <daniel@ffwll.ch>,
	David Airlie <airlied@gmail.com>,
	dri-devel@lists.freedesktop.org,
	Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
	Maxime Ripard <mripard@kernel.org>,
	Thomas Zimmermann <tzimmermann@suse.de>
Subject: Re: [PATCH] drm: zynqmp_dpsub: Always register bridge
Date: Sat, 27 Apr 2024 10:47:20 +0300	[thread overview]
Message-ID: <3d72f876-2bae-495f-8851-bfcce4b827c9@ideasonboard.com> (raw)
In-Reply-To: <20240426093053.GB4524@pendragon.ideasonboard.com>

On 26/04/2024 12:30, Laurent Pinchart wrote:
> On Fri, Mar 22, 2024 at 08:01:44AM +0200, Tomi Valkeinen wrote:
>> On 08/03/2024 22:47, Sean Anderson wrote:
>>> We must always register the DRM bridge, since zynqmp_dp_hpd_work_func
>>> calls drm_bridge_hpd_notify, which in turn expects hpd_mutex to be
>>> initialized. We do this before zynqmp_dpsub_drm_init since that calls
>>> drm_bridge_attach. This fixes the following lockdep warning:
>>>
>>> [   19.217084] ------------[ cut here ]------------
>>> [   19.227530] DEBUG_LOCKS_WARN_ON(lock->magic != lock)
>>> [   19.227768] WARNING: CPU: 0 PID: 140 at kernel/locking/mutex.c:582 __mutex_lock+0x4bc/0x550
>>> [   19.241696] Modules linked in:
>>> [   19.244937] CPU: 0 PID: 140 Comm: kworker/0:4 Not tainted 6.6.20+ #96
>>> [   19.252046] Hardware name: xlnx,zynqmp (DT)
>>> [   19.256421] Workqueue: events zynqmp_dp_hpd_work_func
>>> [   19.261795] pstate: 60000005 (nZCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
>>> [   19.269104] pc : __mutex_lock+0x4bc/0x550
>>> [   19.273364] lr : __mutex_lock+0x4bc/0x550
>>> [   19.277592] sp : ffffffc085c5bbe0
>>> [   19.281066] x29: ffffffc085c5bbe0 x28: 0000000000000000 x27: ffffff88009417f8
>>> [   19.288624] x26: ffffff8800941788 x25: ffffff8800020008 x24: ffffffc082aa3000
>>> [   19.296227] x23: ffffffc080d90e3c x22: 0000000000000002 x21: 0000000000000000
>>> [   19.303744] x20: 0000000000000000 x19: ffffff88002f5210 x18: 0000000000000000
>>> [   19.311295] x17: 6c707369642e3030 x16: 3030613464662072 x15: 0720072007200720
>>> [   19.318922] x14: 0000000000000000 x13: 284e4f5f4e524157 x12: 0000000000000001
>>> [   19.326442] x11: 0001ffc085c5b940 x10: 0001ff88003f388b x9 : 0001ff88003f3888
>>> [   19.334003] x8 : 0001ff88003f3888 x7 : 0000000000000000 x6 : 0000000000000000
>>> [   19.341537] x5 : 0000000000000000 x4 : 0000000000001668 x3 : 0000000000000000
>>> [   19.349054] x2 : 0000000000000000 x1 : 0000000000000000 x0 : ffffff88003f3880
>>> [   19.356581] Call trace:
>>> [   19.359160]  __mutex_lock+0x4bc/0x550
>>> [   19.363032]  mutex_lock_nested+0x24/0x30
>>> [   19.367187]  drm_bridge_hpd_notify+0x2c/0x6c
>>> [   19.371698]  zynqmp_dp_hpd_work_func+0x44/0x54
>>> [   19.376364]  process_one_work+0x3ac/0x988
>>> [   19.380660]  worker_thread+0x398/0x694
>>> [   19.384736]  kthread+0x1bc/0x1c0
>>> [   19.388241]  ret_from_fork+0x10/0x20
>>> [   19.392031] irq event stamp: 183
>>> [   19.395450] hardirqs last  enabled at (183): [<ffffffc0800b9278>] finish_task_switch.isra.0+0xa8/0x2d4
>>> [   19.405140] hardirqs last disabled at (182): [<ffffffc081ad3754>] __schedule+0x714/0xd04
>>> [   19.413612] softirqs last  enabled at (114): [<ffffffc080133de8>] srcu_invoke_callbacks+0x158/0x23c
>>> [   19.423128] softirqs last disabled at (110): [<ffffffc080133de8>] srcu_invoke_callbacks+0x158/0x23c
>>> [   19.432614] ---[ end trace 0000000000000000 ]---
>>>
>>> Fixes: eb2d64bfcc17 ("drm: xlnx: zynqmp_dpsub: Report HPD through the bridge")
>>> Signed-off-by: Sean Anderson <sean.anderson@linux.dev>
>>> ---
>>>
>>>    drivers/gpu/drm/xlnx/zynqmp_dpsub.c | 6 ++----
>>>    1 file changed, 2 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/xlnx/zynqmp_dpsub.c b/drivers/gpu/drm/xlnx/zynqmp_dpsub.c
>>> index 88eb33acd5f0..639fff2c693f 100644
>>> --- a/drivers/gpu/drm/xlnx/zynqmp_dpsub.c
>>> +++ b/drivers/gpu/drm/xlnx/zynqmp_dpsub.c
>>> @@ -256,12 +256,11 @@ static int zynqmp_dpsub_probe(struct platform_device *pdev)
>>>    	if (ret)
>>>    		goto err_dp;
>>>    
>>> +	drm_bridge_add(dpsub->bridge);
> 
> A blank line here would be nice.
> 
>>>    	if (dpsub->dma_enabled) {
>>>    		ret = zynqmp_dpsub_drm_init(dpsub);
>>>    		if (ret)
>>>    			goto err_disp;
>>> -	} else {
>>> -		drm_bridge_add(dpsub->bridge);
>>>    	}
>>>    
>>>    	dev_info(&pdev->dev, "ZynqMP DisplayPort Subsystem driver probed");
>>> @@ -288,9 +287,8 @@ static void zynqmp_dpsub_remove(struct platform_device *pdev)
>>>    
>>>    	if (dpsub->drm)
>>>    		zynqmp_dpsub_drm_cleanup(dpsub);
>>> -	else
>>> -		drm_bridge_remove(dpsub->bridge);
>>>    
>>> +	drm_bridge_remove(dpsub->bridge);
>>>    	zynqmp_disp_remove(dpsub);
>>>    	zynqmp_dp_remove(dpsub);
>>>    
>>
>> I sent a similar patch:
>>
>> https://lore.kernel.org/all/20240312-xilinx-dp-lock-fix-v1-1-1698f9f03bac@ideasonboard.com/
>>
>> I have the drm_bridge_add() call in zynqmp_dp_probe(), as that's where
>> the bridge is set up, so it felt like a logical place. You add it later,
>> just before the bridge is used the first time.
>>
>> I like mine a bit more as it has all the bridge code in the same place,
>> but I also wonder if there might be some risks in adding the bridge
>> early (before zynqmp_disp_probe()), although I can't see any issue right
>> away...
> 
> Seems we have the same concerns :-) I've reviewed your patch and wrote
> pretty much the same. I would be more comfortable with this version,
> even if I like gathering all bridge code in the same location.

I guess there's no reason to take the risk here, so I have pushed this 
one to drm-misc-next.

  Tomi

>> In any case, as this works for me too:
>>
>> Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
> 
> Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> 