linux-kernel - Re: [PATCH v3 03/14] drm/rockchip: analogix_dp: Apply drmm_encoder_init() instead of drm_simple_encoder

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Message-ID: <63226b37-1dec-4998-b2b6-e969ca786f37@rock-chips.com>
Date: Tue, 29 Jul 2025 11:22:49 +0800
From: Damon Ding <damon.ding@...k-chips.com>
To: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
Cc: andrzej.hajda@...el.com, neil.armstrong@...aro.org, rfoss@...nel.org,
 Laurent.pinchart@...asonboard.com, jonas@...boo.se,
 jernej.skrabec@...il.com, maarten.lankhorst@...ux.intel.com,
 mripard@...nel.org, tzimmermann@...e.de, airlied@...il.com, simona@...ll.ch,
 jingoohan1@...il.com, inki.dae@...sung.com, sw0312.kim@...sung.com,
 kyungmin.park@...sung.com, krzk@...nel.org, alim.akhtar@...sung.com,
 hjc@...k-chips.com, heiko@...ech.de, andy.yan@...k-chips.com,
 l.stach@...gutronix.de, dianders@...omium.org,
 dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-samsung-soc@...r.kernel.org,
 linux-rockchip@...ts.infradead.org
Subject: Re: [PATCH v3 03/14] drm/rockchip: analogix_dp: Apply
 drmm_encoder_init() instead of drm_simple_encoder_init()

Hi Dmitry,

On 2025/7/26 8:12, Dmitry Baryshkov wrote:
> On Thu, Jul 24, 2025 at 04:02:53PM +0800, Damon Ding wrote:
>> Compared with drm_simple_encoder_init(), drmm_encoder_init() can handle
>> the cleanup automatically through registering drm_encoder_cleanup() with
>> drmm_add_action().
>>
>> Signed-off-by: Damon Ding <damon.ding@...k-chips.com>
>> ---
>>   drivers/gpu/drm/rockchip/analogix_dp-rockchip.c | 4 +---
>>   1 file changed, 1 insertion(+), 3 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/rockchip/analogix_dp-rockchip.c b/drivers/gpu/drm/rockchip/analogix_dp-rockchip.c
>> index d30f0983a53a..4ed6bf9e5377 100644
>> --- a/drivers/gpu/drm/rockchip/analogix_dp-rockchip.c
>> +++ b/drivers/gpu/drm/rockchip/analogix_dp-rockchip.c
>> @@ -29,7 +29,6 @@
>>   #include <drm/drm_of.h>
>>   #include <drm/drm_panel.h>
>>   #include <drm/drm_probe_helper.h>
>> -#include <drm/drm_simple_kms_helper.h>
>>   
>>   #include "rockchip_drm_drv.h"
>>   
>> @@ -377,8 +376,7 @@ static int rockchip_dp_drm_create_encoder(struct rockchip_dp_device *dp)
>>   							     dev->of_node);
>>   	DRM_DEBUG_KMS("possible_crtcs = 0x%x\n", encoder->possible_crtcs);
>>   
>> -	ret = drm_simple_encoder_init(drm_dev, encoder,
>> -				      DRM_MODE_ENCODER_TMDS);
>> +	ret = drmm_encoder_init(drm_dev, encoder, NULL, DRM_MODE_ENCODER_TMDS, NULL);
> 
> It's not possible to use drmm_encoder_init() here. Per the documentation
> the encoder data structure should be allocated by drmm_kzalloc().
> However this drm_encoder is a part of struct rockchip_dp_device. It's
> allocated by rockchip_dp_probe() via devm_kzalloc(). This means that it
> can potentially be freed before the drm device is completely released,
> creating a use-after-free error.
> 
>>   	if (ret) {
>>   		DRM_ERROR("failed to initialize encoder with drm\n");
>>   		return ret;
>> -- 
>> 2.34.1
>>
> 

Got it. This patch will be dropped in the next version.

Best regards,
Damon