Hi Boris, On 24.12.2019 11:03, Boris Brezillon wrote: > On Tue, 24 Dec 2019 10:49:36 +0100 > Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx> wrote: >> On Tue, 24 Dec 2019 10:44:22 +0100 >> Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx> wrote: >>> On Tue, 24 Dec 2019 10:16:49 +0100 >>> Andrzej Hajda <a.hajda@xxxxxxxxxxx> wrote: >>>> On 23.12.2019 10:55, Marek Szyprowski wrote: >>>>> On 16.12.2019 16:25, Boris Brezillon wrote: >>>>>> On Mon, 16 Dec 2019 16:02:36 +0100 >>>>>> Marek Szyprowski <m.szyprowski@xxxxxxxxxxx> wrote: >>>>>>> On 16.12.2019 15:55, Boris Brezillon wrote: >>>>>>>> On Mon, 16 Dec 2019 14:54:25 +0100 >>>>>>>> Marek Szyprowski <m.szyprowski@xxxxxxxxxxx> wrote: >>>>>>>>> On 03.12.2019 15:15, Boris Brezillon wrote: >>>>>>>>>> So that each element in the chain can easily access its predecessor. >>>>>>>>>> This will be needed to support bus format negotiation between elements >>>>>>>>>> of the bridge chain. >>>>>>>>>> >>>>>>>>>> Signed-off-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx> >>>>>>>>>> Reviewed-by: Neil Armstrong <narmstrong@xxxxxxxxxxxx> >>>>>>>>>> Reviewed-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> >>>>>>>>> I've noticed that this patch got merged to linux-next as commit >>>>>>>>> 05193dc38197021894b17239fafbd2eb1afe5a45. Sadly it breaks booting of >>>>>>>>> Samsung Exynos5250-based Arndale board. Booting stops after following >>>>>>>>> messages: >>>>>>>>> >>>>>>>>> [drm] Exynos DRM: using 14400000.fimd device for DMA mapping operations >>>>>>>>> exynos-drm exynos-drm: bound 14400000.fimd (ops fimd_component_ops) >>>>>>>>> exynos-drm exynos-drm: bound 14450000.mixer (ops mixer_component_ops) >>>>>>>>> exynos-drm exynos-drm: bound 14500000.dsi (ops exynos_dsi_component_ops) >>>>>>>>> exynos-drm exynos-drm: bound 14530000.hdmi (ops hdmi_component_ops) >>>>>>>>> [drm] Supports vblank timestamp caching Rev 2 (21.10.2013). >>>>>>>>> [drm] No driver support for vblank timestamp query. >>>>>>>>> [drm] Cannot find any crtc or sizes >>>>>>>>> [drm] Cannot find any crtc or sizes >>>>>>>>> [drm] Initialized exynos 1.1.0 20180330 for exynos-drm on minor 0 >>>>>>>>> >>>>>>>>> I will try to debug this and provide more information soon. >>>>>>>>> >>>>>>>> Can you try with this diff applied? >>>>>>> This patch doesn't change anything. >>>>>> Okay. Can you do a list_for_each_entry() on both encoder->bridge_chain >>>>>> and dsi->bridge_chain (dump bridge pointers in a pr_info()) before and >>>>>> after the list_splice_init() call? >>>>> encoder->bridge_chain contains only one element. dsi->drive_chain is empty. >>>>> >>>>> Replacing that list_splice() with INIT_LIST_HEAD(&encoder->bridge_chain) >>>>> fixed the boot issue. >>> If INIT_LIST_HEAD() worked, I don't understand why replacing the >>> list_splice() call by a list_splice_init() (which doing a list_splice() >>> + INIT_LIST_HEAD()) didn't fix the problem. Are you sure the >>> list_splice_init() version doesn't work? >>> >>>>> It looks that this is related with the way the >>>>> Exynos DSI handles bridges (in bridge and out brige?). Maybe Andrzej >>>>> will give a bit more detailed comment and spread some light on this. >>>> >>>> Hi Marek, Boris, >>>> >>>> >>>> I have not followed latest patches due to high work load, my bad. Marek >>>> thanks from pointing >>>> >>>> About ExynosDSI bridge handling: >>>> >>>> The order of calling encoder, bridge (and consequently panel) ops >>>> enforced by DRM core (bridge->pre_enable, encoder->enable, >>>> bridge->enable) does not fit to ExynosDSI hardware initialization >>>> sequence, if I remember correctly it does not fit to whole MIPI DSI >>>> standard (I think similar situation is with eDP). As a result DSI >>>> drivers must use some ugly workarounds, rely on HW properly coping with >>>> incorrect sequences, or, as in case of ExynosDSI driver, just avoid >>>> using encoder->bridge chaining and call bridge ops by itself when suitable. >>> Yes, that's definitely hack-ish, and I proposed 2 solutions to address >>> that in previous versions of this patchset, unfortunately I didn't get >>> any feedback so I went for the less invasive option (keep the hack but >>> adapt it to the double-linked list changes), which still lead to >>> regressions :-/. >>> >>> Just a reminder of my 2 proposals: >>> >>> 1/ implement the bridge_ops->pre_enable/post_disable() hooks so you can >>> split your enable/disable logic in 2 parts and make sure things are >>> ready when the panel/next bridge tries to send DSI commands >>> 2/ move everything that's needed to send DSI commands out of the >>> ->enable() path (maybe in runtime PM resume/suspend hooks) so you >>> can call that in the DSI transfer path too >>> >>> As pointed out by Laurent, #1 doesn't work because some panel drivers >>> send DSI commands in their ->prepare() hook, and ->pre_enable() methods >>> are called in reverse order, meaning that the DRM panel bridge driver >>> would try to issue DSI commands before the DSI host controllers is ready >>> to send them. I still thing #2 is a good option. >>> >>>> So proper patch converting to double-linked list should not try to >>>> splice ExynosDSI private bridge list with with encoder's, encoder's list >>>> should be always empty, as Marek suggested. >>> That's exactly what I wanted to do: make the encoder's list empty after >>> attach() and restore it to its initial state before unregistering >>> the bridge, except I forgot that list_splice() doesn't call >>> INIT_LIST_HEAD(). It's still not clear to me why replacing the >>> list_splice() call by a list_splice_init() didn't work. >> Okay, I think I figured it out: drm_bridge_chain_xx() helpers use >> encoder->bridge_chain as their list head, and you'll never hit the 'elem >> is list head' condition since we moved all elems from >> encoder->bridge_chain to exynos_dsi->bridge_chain. The only way this >> can work is if we stop using the helpers and implement our own list >> iterators. > Just to make it clear, calling INIT_LIST_HEAD(encoder->bridge_chain) > doesn't really fix the bug, it just prevents the hang (infinite loop) > and turn all drm_bridge_chain_xx() calls into NOPs. Right, I've just checked it and indeed the display chain outputs nothing after such 'fix'. To get it finally working I've replaced drm_bridge_chain_*() operations for exynos_dsi 'out_bridge' by a direct calls. I will submit a patch in a few minutes. I hope that such workaround can be used now to fix the regression until a better solution is agreed. Best regards -- Marek Szyprowski, PhD Samsung R&D Institute Poland
