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: > > > Hi Boris, > > > > > > On 16.12.2019 16:25, Boris Brezillon wrote: > > >> On Mon, 16 Dec 2019 16:02:36 +0100 > > >> Marek Szyprowski <m.szyprowski@xxxxxxxxxxx> wrote: > > >>> Hi Boris, > > >>> > > >>> 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.
