Re: [PATCH v3 03/14] drm/rockchip: analogix_dp: Apply drmm_encoder_init() instead of drm_simple_encoder_init()

From: Damon Ding <damon.ding@rock-chips.com>
To: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Cc: andrzej.hajda@intel.com, neil.armstrong@linaro.org,
	rfoss@kernel.org, Laurent.pinchart@ideasonboard.com,
	jonas@kwiboo.se, jernej.skrabec@gmail.com,
	maarten.lankhorst@linux.intel.com, mripard@kernel.org,
	tzimmermann@suse.de, airlied@gmail.com, simona@ffwll.ch,
	jingoohan1@gmail.com, inki.dae@samsung.com,
	sw0312.kim@samsung.com, kyungmin.park@samsung.com,
	krzk@kernel.org, alim.akhtar@samsung.com, hjc@rock-chips.com,
	heiko@sntech.de, andy.yan@rock-chips.com, l.stach@pengutronix.de,
	dianders@chromium.org, dri-devel@lists.freedesktop.org,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-samsung-soc@vger.kernel.org,
	linux-rockchip@lists.infradead.org
Subject: Re: [PATCH v3 03/14] drm/rockchip: analogix_dp: Apply drmm_encoder_init() instead of drm_simple_encoder_init()
Date: Tue, 29 Jul 2025 11:22:49 +0800	[thread overview]
Message-ID: <63226b37-1dec-4998-b2b6-e969ca786f37@rock-chips.com> (raw)
In-Reply-To: <6psjcrhbnk7czdrdtxh65kr6qvygkwogvert75dg2svbm2cqd3@uhffyfdxqpec>

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@rock-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

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