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

[Sean Anderson]

Hi,

On 3/22/24 02:01, Tomi Valkeinen wrote:
> Hi,
> 
> 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@xxxxxxxxx>
>> ---
>>
>>   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);
>>       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@xxxxxxxxxxxxxxxx/
> 
> 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...
> 
> In any case, as this works for me too:
> 
> Reviewed-by: Tomi Valkeinen <tomi.valkeinen@xxxxxxxxxxxxxxxx>
> 
>  Tomi
> 
Can someone pick up this fix before the release? I am still running into this bug on linux-next/master.

--Sean