On Fri, Apr 27, 2018 at 01:40:21AM +0300, Laurent Pinchart wrote: > Hi Peter, > > Thank you for the patches. > > On Friday, 27 April 2018 01:31:15 EEST Peter Rosin wrote: > > Hi! > > > > It was noted by Russel King [1] that bridges (not using components) > > might disappear unexpectedly if the owner of the bridge was unbound. > > Jyri Sarha had previously noted the same thing with panels [2]. Jyri > > came up with using device links to resolve the panel issue, which > > was also my (independent) reaction to the note from Russel. > > > > This series builds up to the addition of that link in the last > > patch, but in my opinion the other 23 patches do have merit on their > > own. > > > > The last patch needs testing, while the others look trivial. That > > said, I might have missed some subtlety. > > I don't think this is the way to go. We have a real lifetime management > problem with bridges, and device links are just trying to hide the problem > under the carpet. They will further corner us by making a real fix much more > difficult to implement. I'll try to comment further in the next few days on > what I think a better solution would be, but in a nutshell I believe that > drm_bridge objects need to be refcounted, with a .release() operation to free > the bridge resources when the reference count drops to zero. This shouldn't be > difficult to implement and I'm willing to help. I agree that refcounting is the proper fix if bridges can be hot-unplugged, independently of the overall drm_device. And yes retro-shoehorning refcounting is "fun", but it's also not impossible. I've done it a few times by now in drm. Otoh, refcounting has a pretty serious cost - we're still blowing up drm_framebuffer refcounting in corner cases at shocking regularity, and that's something that's been refcounted for years by now. As long as we don't have a clearly defined need to make bridges hotpluggable then I think not paying the hefty bill just yet is the correct technical decision. This patch series here looks like a reasonable way to tie the lifetimes together a bit more closely and should fix the bugs we have right now. Cheers, Daniel PS: Yes there's cases where you can hotplug display blocks on a SoC. To my knowledge they're all covered by hotplugging the entire drm_device (plus all the statically associated bits like drm_bridge/crtc/plane/encoder). And we're already working on fixing up drm_device to at least make it possible to write a correct hot-unpluggable driver in theory. We'll see whether anyone manages to pull that off in practice :-) > > > [1] https://lkml.org/lkml/2018/4/23/769 > > [2] https://www.spinics.net/lists/dri-devel/msg174275.html > > > > Peter Rosin (24): > > drm/bridge: allow optionally specifying an .owner device > > drm/bridge: adv7511: provide an .owner device > > drm/bridge/analogix: core: specify the .owner of the bridge > > drm/bridge: analogix-anx78xx: provide an .owner device > > drm/bridge: vga-dac: provide an .owner device > > drm/bridge: lvds-encoder: provide an .owner device > > drm/bridge: megachips-stdpxxxx-ge-b850v3-fw: provide an .owner device > > drm/bridge: nxp-ptn3460: provide an .owner device > > drm/bridge: panel: provide an .owner device > > drm/bridge: ps8622: provide an .owner device > > drm/bridge: sii902x: provide an .owner device > > drm/bridge: sii9234: provide an .owner device > > drm/bridge: sii8620: provide an .owner device > > drm/bridge: synopsys: provide an .owner device for the bridges > > drm/bridge: tc358767: provide an .owner device > > drm/bridge: ti-tfp410: provide an .owner device > > drm/exynos: mic: provide an .owner device for the bridge > > drm/mediatek: hdmi: provide an .owner device for the bridge > > drm/msm: specify the .owner of the bridges > > drm/rcar-du: lvds: provide an .owner device for the bridge > > drm/sti: provide an .owner device for the bridges > > drm/bridge: remove the .of_node member > > drm/bridge: require the .owner to be filled in on drm_bridge_attach > > drm/bridge: establish a link between the bridge supplier and consumer > > > > drivers/gpu/drm/bridge/adv7511/adv7511_drv.c | 2 +- > > drivers/gpu/drm/bridge/analogix-anx78xx.c | 5 +---- > > drivers/gpu/drm/bridge/analogix/analogix_dp_core.c | 1 + > > drivers/gpu/drm/bridge/dumb-vga-dac.c | 2 +- > > drivers/gpu/drm/bridge/lvds-encoder.c | 2 +- > > .../drm/bridge/megachips-stdpxxxx-ge-b850v3-fw.c | 2 +- > > drivers/gpu/drm/bridge/nxp-ptn3460.c | 2 +- > > drivers/gpu/drm/bridge/panel.c | 4 +--- > > drivers/gpu/drm/bridge/parade-ps8622.c | 2 +- > > drivers/gpu/drm/bridge/sii902x.c | 2 +- > > drivers/gpu/drm/bridge/sii9234.c | 2 +- > > drivers/gpu/drm/bridge/sil-sii8620.c | 2 +- > > drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 4 +--- > > drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c | 4 +--- > > drivers/gpu/drm/bridge/tc358767.c | 2 +- > > drivers/gpu/drm/bridge/ti-tfp410.c | 2 +- > > drivers/gpu/drm/drm_bridge.c | 23 ++++++++++++++++++- > > drivers/gpu/drm/exynos/exynos_drm_mic.c | 2 +- > > drivers/gpu/drm/mediatek/mtk_hdmi.c | 2 +- > > drivers/gpu/drm/msm/dsi/dsi_manager.c | 1 + > > drivers/gpu/drm/msm/edp/edp_bridge.c | 1 + > > drivers/gpu/drm/msm/hdmi/hdmi_bridge.c | 1 + > > drivers/gpu/drm/rcar-du/rcar_lvds.c | 2 +- > > drivers/gpu/drm/sti/sti_dvo.c | 2 +- > > drivers/gpu/drm/sti/sti_hda.c | 1 + > > drivers/gpu/drm/sti/sti_hdmi.c | 1 + > > include/drm/drm_bridge.h | 8 ++++---- > > 27 files changed, 51 insertions(+), 33 deletions(-) > > > -- > Regards, > > Laurent Pinchart > > > > _______________________________________________ > dri-devel mailing list > dri-devel@xxxxxxxxxxxxxxxxxxxxx > https://lists.freedesktop.org/mailman/listinfo/dri-devel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch -- To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
