On Fri, 27 Dec 2019 15:41:24 +0100
Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx> 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 Exynos 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
> the list_splice() call by list_splice_init() 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 exynos_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@xxxxxxxxxxx>
> Fixes: 05193dc38197 ("drm/bridge: Make the bridge chain a double-linked list")
> Signed-off-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>
> ---
> Hello Marek,
>
> I'm perfectly fine applying your patch instead of this one if you prefer
> to restrict the logic to a single bridge per chain. I just sent this
> patch in case your okay with the slightly different version I propose
> here.
Marek, Andrzej, did you have time to look at this patch (or respin
"drm/bridge: Fix Exynos DSI after making bridge chain a double-linked
list" if you don't like this version)?
I'd really like to apply this fix (and its vc4 equivalent) to
drm-misc-next as soon as possible.
Thanks,
Boris
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