[PATCH 2/3] drm/vc4: dsi: Fix bridge chain handling

[Andrzej Hajda]

On 27.12.2019 15:41, Boris Brezillon wrote:
> Commit 05193dc38197 ("drm/bridge: Make the bridge chain a double-linked
> list") patched the bridge chain logic to use a double-linked list instead
> of a single-linked list. This change induced changes to the VC4 driver
> which was manually resetting the encoder->bridge element to NULL to
> control the enable/disable sequence of the bridge chain. During this
> conversion, 2 bugs were introduced:
>
> 1/ list_splice() was used to move chain elements to our own internal
>    chain, but list_splice() does not reset the source list to an empty
>    state, leading to unexpected bridge hook calls when
>    drm_bridge_chain_xxx() helpers were called by the core. Replacing
>    those list_splice() calls by list_splice_init() ones fixes this
>    problem.
>
> 2/ drm_bridge_chain_xxx() helpers operate on the
>    bridge->encoder->bridge_chain list, which is now empty. When the
>    helper uses list_for_each_entry_reverse() we end up with no operation
>    done which is not what we want. But that's even worse when the helper
>    uses list_for_each_entry_from(), because in that case we end up in
>    an infinite loop searching for the list head element which is no
>    longer encoder->bridge_chain but vc4_dsi->bridge_chain. To address
>    that problem we stop using the bridge chain helpers and call the
>    hooks directly.
>
> Reported-by: Marek Szyprowski <m.szyprowski at samsung.com>
> Cc: Eric Anholt <eric at anholt.net>
> Fixes: 05193dc38197 ("drm/bridge: Make the bridge chain a double-linked list")
> Signed-off-by: Boris Brezillon <boris.brezillon at collabora.com>
Reviewed-by: Andrzej Hajda <a.hajda at samsung.com>

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Regards
Andrzej