Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.34 as permitted sender) client-ip=23.128.96.34;
MIME-Version: 1.0
Date:   Fri, 01 Dec 2023 10:04:33 +0100
From:   Michael Walle <mwalle@kernel.org>
To:     Inki Dae <inki.dae@samsung.com>,
        Jagan Teki <jagan@amarulasolutions.com>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Andrzej Hajda <andrzej.hajda@intel.com>,
        Neil Armstrong <neil.armstrong@linaro.org>,
        Robert Foss <rfoss@kernel.org>,
        Laurent Pinchart <Laurent.pinchart@ideasonboard.com>,
        Jonas Karlman <jonas@kwiboo.se>,
        Jernej Skrabec <jernej.skrabec@gmail.com>,
        David Airlie <airlied@gmail.com>,
        Daniel Vetter <daniel@ffwll.ch>,
        Frieder Schrempf <frieder.schrempf@kontron.de>,
        Tim Harvey <tharvey@gateworks.com>,
        Alexander Stein <alexander.stein@ew.tq-group.com>
Cc:     dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] drm: bridge: samsung-dsim: Don't use FORCE_STOP_STATE
In-Reply-To: <20231113164344.1612602-1-mwalle@kernel.org>
References: <20231113164344.1612602-1-mwalle@kernel.org>
Message-ID: <631fe35a2a3b00781231e4f3f5094fae@kernel.org>
Content-Type: text/plain; charset=US-ASCII;
 format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk

> The FORCE_STOP_STATE bit is unsuitable to force the DSI link into LP-11
> mode. It seems the bridge internally queues DSI packets and when the
> FORCE_STOP_STATE bit is cleared, they are sent in close succession
> without any useful timing (this also means that the DSI lanes won't go
> into LP-11 mode). The length of this gibberish varies between 1ms and
> 5ms. This sometimes breaks an attached bridge (TI SN65DSI84 in this
> case). In our case, the bridge will fail in about 1 per 500 reboots.
> 
> The FORCE_STOP_STATE handling was introduced to have the DSI lanes in
> LP-11 state during the .pre_enable phase. But as it turns out, none of
> this is needed at all. Between samsung_dsim_init() and
> samsung_dsim_set_display_enable() the lanes are already in LP-11 mode.
> The code as it was before commit 20c827683de0 ("drm: bridge:
> samsung-dsim: Fix init during host transfer") and 0c14d3130654 ("drm:
> bridge: samsung-dsim: Fix i.MX8M enable flow to meet spec") was correct
> in this regard.
> 
> This patch basically reverts both commits. It was tested on an i.MX8M
> SoC with an SN65DSI84 bridge. The signals were probed and the DSI
> packets were decoded during initialization and link start-up. After 
> this
> patch the first DSI packet on the link is a VSYNC packet and the timing
> is correct.
> 
> Command mode between .pre_enable and .enable was also briefly tested by
> a quick hack. There was no DSI link partner which would have responded,
> but it was made sure the DSI packet was send on the link. As a side
> note, the command mode seems to just work in HS mode. I couldn't find
> that the bridge will handle commands in LP mode.
> 
> Fixes: 20c827683de0 ("drm: bridge: samsung-dsim: Fix init during host 
> transfer")
> Fixes: 0c14d3130654 ("drm: bridge: samsung-dsim: Fix i.MX8M enable flow 
> to meet spec")
> Signed-off-by: Michael Walle <mwalle@kernel.org>
> ---
> Let me know wether this should be two commits each reverting one, but 
> both
> commits appeared first in kernel 6.5.

Are there any news?

-michael