linux-kernel - Re: [PATCH] drm: zynqmp_dpsub: Always register bridge

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Message-ID: <222c0245-b8bc-48d8-b4e1-a9fb276774ae@ideasonboard.com>
Date: Fri, 22 Mar 2024 08:01:44 +0200
From: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
To: 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>,
 Laurent Pinchart <laurent.pinchart@...asonboard.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

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@...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);
>   	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...

In any case, as this works for me too:

Reviewed-by: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>

  Tomi