Re: [PATCH 3/3] drm/exynos: dsi: Fix bridge chain handling

[Boris Brezillon <boris.brezillon@collabora.com>]

On Fri, 27 Dec 2019 15:41:24 +0100
Boris Brezillon <boris.brezillon@collabora.com> 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@samsung.com>
> Fixes: 05193dc38197 ("drm/bridge: Make the bridge chain a double-linked list")
> Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
> ---
> 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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