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Date: Sat, 27 Apr 2024 10:47:20 +0300
From: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
To: Laurent Pinchart <laurent.pinchart@...asonboard.com>,
Sean Anderson <sean.anderson@...ux.dev>
Cc: linux-arm-kernel@...ts.infradead.org, Michal Simek
<michal.simek@....com>, linux-kernel@...r.kernel.org,
Daniel Vetter <daniel@...ll.ch>, David Airlie <airlied@...il.com>,
dri-devel@...ts.freedesktop.org,
Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>
Subject: Re: [PATCH] drm: zynqmp_dpsub: Always register bridge
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@...ux.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@...asonboard.com>
>
> Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
>
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