linux-kernel - Re: [PATCH] drm/mediatek: mtk_dsi: Avoid EPROBE

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Date:   Tue, 4 Jan 2022 10:13:44 +0100
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     dri-devel@...ts.freedesktop.org
Cc:     linux-mediatek@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        chunkuang.hu@...nel.org, p.zabel@...gutronix.de, airlied@...ux.ie,
        daniel@...ll.ch, matthias.bgg@...il.com, kernel@...labora.com
Subject: Re: [PATCH] drm/mediatek: mtk_dsi: Avoid EPROBE_DEFER loop with
 external bridge

Il 10/12/21 12:36, AngeloGioacchino Del Regno ha scritto:
> DRM bridge drivers are now attaching their DSI device at probe time,
> which requires us to register our DSI host in order to let the bridge
> to probe: this recently started producing an endless -EPROBE_DEFER
> loop on some machines that are using external bridges, like the
> parade-ps8640, found on the ACER Chromebook R13.
> 
> Now that the DSI hosts/devices probe sequence is documented, we can
> do adjustments to the mtk_dsi driver as to both fix now and make sure
> to avoid this situation in the future: for this, following what is
> documented in drm_bridge.c, move the mtk_dsi component_add() to the
> mtk_dsi_ops.attach callback and delete it in the detach callback;
> keeping in mind that we are registering a drm_bridge for our DSI,
> which is only used/attached if the DSI Host is bound, it wouldn't
> make sense to keep adding our bridge at probe time (as it would
> be useless to have it if mtk_dsi_ops.attach() fails!), so also move
> that one to the dsi host attach function (and remove it in detach).
> 
> Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>

Due to the latest changes in drm bridge, we need this patch to land as soon as
possible, otherwise breakages will be seen on all MediaTek powered devices using
DSI to eDP/DP bridges...

...hence, friendly ping for a review :)