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Date: Fri, 12 Sep 2014 20:24:41 +0900 From: Inki Dae <inki.dae@...sung.com> To: Andrzej Hajda <a.hajda@...sung.com> Cc: "moderated list:ARM/S5P EXYNOS AR..." <linux-samsung-soc@...r.kernel.org>, Seung-Woo Kim <sw0312.kim@...sung.com>, open list <linux-kernel@...r.kernel.org>, dri-devel@...ts.freedesktop.org, Kyungmin Park <kyungmin.park@...sung.com>, Marek Szyprowski <m.szyprowski@...sung.com> Subject: Re: [PATCH 5/9] drm/exynos/crtc: fix framebuffer reference sequence On 2014년 09월 12일 20:04, Andrzej Hajda wrote: > On 09/12/2014 12:45 PM, Inki Dae wrote: >> On 2014년 09월 12일 18:27, Andrzej Hajda wrote: >>> On 09/12/2014 10:57 AM, Daniel Vetter wrote: >>>> On Fri, Sep 12, 2014 at 05:34:50PM +0900, Inki Dae wrote: >>>>> 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. >>>> Generally it's not a good idea to drop fb references from irq context, >>>> since if you actually drop the last reference it'll blow up: fb cleanup >>>> needs a bunch of mutexes. >>> I agree with that. >>> >>>> Also the drm core really should be taking care of this for you, you only >>>> need to grab references yourself for async flips if you want the buffer to >>>> survive a bit. crtc_mode_set has not need for this. I expect that the >>>> refcounting bug is somewhere else, at least from my experience chasing >>>> such issues in i915 ;-) >>> Hmm, maybe I miss something but I do not see the core grabbing fb reference >>> on plane->fb update. On the other side drm_framebuffer_remove calls >>> drm_plane_force_disable which drops plane->fb reference. >>> I am not yet familiar with this code so maybe there is better solution. >>> >>> If not I guess it would be better to move this code to >>> exynos_plane_mode_set. >>> At least it is done this way in omap and msm, in fact it seems better place >> I cannot see it in msm. In case of msm, drm flip queue is used in >> mdp4/5_crtc_mode_set function. See update_fb function there. > > fb reference dance for planes is in mdp*_plane_update. > > Regarding drm flip in msm old fb unreferencing is done via > drm_flip_work_queue. Yes, that is what drm flip queue does and I mentioned earlier below, http://www.mail-archive.com/linux-kernel@vger.kernel.org/msg724161.html I think we have a talk about how we have to drop a reference to old_fb. Thanks, Inki Dae > > Regards > Andrzej > >> >>> for such things. What do you think? >>> >>> Regards >>> Andrzej >>> >>>> -Daniel >>> -- >>> To unsubscribe from this list: send the line "unsubscribe linux-samsung-soc" in >>> the body of a message to majordomo@...r.kernel.org >>> More majordomo info at http://vger.kernel.org/majordomo-info.html >>> >> > > -- > To unsubscribe from this list: send the line "unsubscribe linux-samsung-soc" in > the body of a message to majordomo@...r.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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