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References: <20220104095954.10313-1-angelogioacchino.delregno@collabora.com>
In-Reply-To: <20220104095954.10313-1-angelogioacchino.delregno@collabora.com>
From:   Jagan Teki <jagan@amarulasolutions.com>
Date:   Wed, 12 Jan 2022 12:39:46 +0530
Message-ID: <CAMty3ZAojTyw3H8VprH9aiyTyWjeL8oqPxNNr=J33_5FrcUj9Q@mail.gmail.com>
Subject: Re: [PATCH v2] drm/mediatek: mtk_dsi: Avoid EPROBE_DEFER loop with
 external bridge
To:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@collabora.com>
Cc:     dri-devel@lists.freedesktop.org, chunkuang.hu@kernel.org,
        airlied@linux.ie, linux-kernel@vger.kernel.org,
        andrzej.hajda@intel.com, linux-mediatek@lists.infradead.org,
        matthias.bgg@gmail.com, kernel@collabora.com,
        linux-arm-kernel@lists.infradead.org
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On Tue, Jan 4, 2022 at 3:30 PM AngeloGioacchino Del Regno
<angelogioacchino.delregno@collabora.com> wrote:
>
> 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@collabora.com>
> Reviewed-by: Andrzej Hajda <andrzej.hajda@intel.com>
> ---

Eventually I've observed similar issue on other Component based DSI
controllers, hence

Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>