linux-kernel - Re: [PATCH 5/9] drm/exynos/crtc: fix framebuffer reference sequence

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Message-id: <5412B02A.6040609@samsung.com>
Date:	Fri, 12 Sep 2014 17:34:50 +0900
From:	Inki Dae <inki.dae@...sung.com>
To:	Andrzej Hajda <a.hajda@...sung.com>
Cc:	Marek Szyprowski <m.szyprowski@...sung.com>,
	Joonyoung Shim <jy0922.shim@...sung.com>,
	Seung-Woo Kim <sw0312.kim@...sung.com>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	dri-devel@...ts.freedesktop.org,
	open list <linux-kernel@...r.kernel.org>,
	"moderated list:ARM/S5P EXYNOS AR..." 
	<linux-samsung-soc@...r.kernel.org>
Subject: Re: [PATCH 5/9] drm/exynos/crtc: fix framebuffer reference sequence

Hi Andrzej,

On 2014년 09월 09일 22:16, Andrzej Hajda wrote:
> Adding reference to framebuffer should be accompanied with removing
> reference to old framebuffer assigned to the plane.
> This patch removes following warning:
> 
> [   95.038017] WARNING: CPU: 1 PID: 3067 at drivers/gpu/drm/drm_crtc.c:5115 drm_mode_config_cleanup+0x258/0x268()
> [   95.048086] Modules linked in:
> [   95.051430] CPU: 1 PID: 3067 Comm: bash Tainted: G        W      3.16.0-11355-g7a6eca5-dirty #3015
> [   95.060058] [<c0013e90>] (unwind_backtrace) from [<c0011128>] (show_stack+0x10/0x14)
> [   95.067766] [<c0011128>] (show_stack) from [<c04a5dc4>] (dump_stack+0x70/0xbc)
> [   95.074953] [<c04a5dc4>] (dump_stack) from [<c0021784>] (warn_slowpath_common+0x64/0x88)
> [   95.083005] [<c0021784>] (warn_slowpath_common) from [<c00217c4>] (warn_slowpath_null+0x1c/0x24)
> [   95.091780] [<c00217c4>] (warn_slowpath_null) from [<c0275fa0>] (drm_mode_config_cleanup+0x258/0x268)
> [   95.100983] [<c0275fa0>] (drm_mode_config_cleanup) from [<c0281724>] (exynos_drm_unload+0x38/0x50)
> [   95.109915] [<c0281724>] (exynos_drm_unload) from [<c026e248>] (drm_dev_unregister+0x24/0x98)
> [   95.118414] [<c026e248>] (drm_dev_unregister) from [<c026ecb0>] (drm_put_dev+0x28/0x64)
> [   95.126412] [<c026ecb0>] (drm_put_dev) from [<c02947c4>] (take_down_master+0x24/0x44)
> [   95.134218] [<c02947c4>] (take_down_master) from [<c0294870>] (component_del+0x8c/0xc8)
> [   95.142201] [<c0294870>] (component_del) from [<c0286c10>] (exynos_dsi_remove+0x18/0x2c)
> [   95.150294] [<c0286c10>] (exynos_dsi_remove) from [<c0299e04>] (platform_drv_remove+0x18/0x1c)
> [   95.158872] [<c0299e04>] (platform_drv_remove) from [<c02987a4>] (__device_release_driver+0x70/0xc4)
> [   95.167981] [<c02987a4>] (__device_release_driver) from [<c0298818>] (device_release_driver+0x20/0x2c)
> [   95.177268] [<c0298818>] (device_release_driver) from [<c02979d0>] (unbind_store+0x5c/0x94)
> [   95.185597] [<c02979d0>] (unbind_store) from [<c0297278>] (drv_attr_store+0x20/0x2c)
> [   95.193323] [<c0297278>] (drv_attr_store) from [<c012aa90>] (sysfs_kf_write+0x4c/0x50)
> [   95.201224] [<c012aa90>] (sysfs_kf_write) from [<c0129e94>] (kernfs_fop_write+0xc4/0x184)
> [   95.209393] [<c0129e94>] (kernfs_fop_write) from [<c00d03ec>] (vfs_write+0xa0/0x1a8)
> [   95.217111] [<c00d03ec>] (vfs_write) from [<c00d07f8>] (SyS_write+0x40/0x8c)
> [   95.224146] [<c00d07f8>] (SyS_write) from [<c000e660>] (ret_fast_syscall+0x0/0x48)
> 
> Signed-off-by: Andrzej Hajda <a.hajda@...sung.com>
> ---
>  drivers/gpu/drm/exynos/exynos_drm_crtc.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/gpu/drm/exynos/exynos_drm_crtc.c b/drivers/gpu/drm/exynos/exynos_drm_crtc.c
> index b68e58f..bde19f4 100644
> --- a/drivers/gpu/drm/exynos/exynos_drm_crtc.c
> +++ b/drivers/gpu/drm/exynos/exynos_drm_crtc.c
> @@ -145,10 +145,16 @@ exynos_drm_crtc_mode_set(struct drm_crtc *crtc, struct drm_display_mode *mode,
>  	if (ret)
>  		return ret;
>  
> +	/* we need to unreference current fb after replacing it with new one */
> +	old_fb = plane->fb;
> +
>  	plane->crtc = crtc;
>  	plane->fb = crtc->primary->fb;
>  	drm_framebuffer_reference(plane->fb);
>  
> +	if (old_fb)
> +		drm_framebuffer_unreference(old_fb);

This time would be a good chance that we can consider drm flip queue to
make sure that whole memory region to old_fb is scanned out completely
before dropping a reference of old_fb. the reference of old_fb should be
dropped at irq handler of each crtc devices, fimd and mixer.

Thanks,
Inki Dae

> +
>  	return 0;
>  }
>  
> 

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