Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <f4c75653-a293-9060-5739-5a244841754c@denx.de>
Date:   Wed, 2 Aug 2023 19:26:08 +0200
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.13.1
Subject: Re: [PATCH] Revert "drm/bridge: lt9611: Do not generate HFP/HBP/HSA
 and EOT packet"
Content-Language: en-US
To:     Dmitry Baryshkov <dmitry.baryshkov@linaro.org>,
        Neil Armstrong <neil.armstrong@linaro.org>,
        Andrzej Hajda <andrzej.hajda@intel.com>,
        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>
Cc:     dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org,
        Jagan Teki <jagan@amarulasolutions.com>,
        Abhinav Kumar <quic_abhinavk@quicinc.com>,
        Amit Pundir <amit.pundir@linaro.org>
References: <20230802-revert-do-not-generate-hfp-hbp-hsa-eot-packet-v1-1-f8a20084e15a@linaro.org>
 <6cd079a4-2f5b-0169-cbaf-b59a72f1b32b@denx.de>
 <ce99a777-10cc-f380-65c8-ef76843ca181@linaro.org>
From:   Marek Vasut <marex@denx.de>
In-Reply-To: <ce99a777-10cc-f380-65c8-ef76843ca181@linaro.org>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 8/2/23 14:38, Dmitry Baryshkov wrote:
> On 02/08/2023 15:07, Marek Vasut wrote:
>> On 8/2/23 10:52, Neil Armstrong wrote:
>>> This reverts commit [1] to fix display regression on the Dragonboard 
>>> 845c
>>> (SDM845) devboard.
>>>
>>> There's a mismatch on the real action of the following flags:
>>> - MIPI_DSI_MODE_VIDEO_NO_HSA
>>> - MIPI_DSI_MODE_VIDEO_NO_HFP
>>> - MIPI_DSI_MODE_VIDEO_NO_HBP
>>> which leads to a non-working display on qcom platforms.
>>>
>>> [1] 8ddce13ae696 ("drm/bridge: lt9611: Do not generate HFP/HBP/HSA 
>>> and EOT packet")
>>>
>>> Cc: Marek Vasut <marex@denx.de>
>>> Cc: Robert Foss <rfoss@kernel.org>
>>> Cc: Jagan Teki <jagan@amarulasolutions.com>
>>> Cc: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
>>> Cc: Abhinav Kumar <quic_abhinavk@quicinc.com>
>>> Fixes: 8ddce13ae69 ("drm/bridge: lt9611: Do not generate HFP/HBP/HSA 
>>> and EOT packet")
>>> Reported-by: Amit Pundir <amit.pundir@linaro.org>
>>> Link: 
>>> https://lore.kernel.org/r/CAMi1Hd0TD=2z_=bcDrht3H_wiLvAFcv8Z-U_r_KUOoeMc6UMjw@mail.gmail.com/
>>> Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
>>
>> This breaks LT9611 operation on i.MX8M Mini/Nano/Plus, so, NAK.
>>
>> I am currently using this LT9611 with Linux 6.1.y in production and 
>> this is not acceptable. I also believe the correct fix is on the MSM 
>> side, not on the LT9611 driver side, since MSM incorrectly implements 
>> these flags.
> 
> Up to now we saw no proof that MSM incorrectly implements the flags.

Please read the whole "[PATCH 2/2] drm/bridge: lt9611: Do not generate 
HFP/HBP/HSA and EOT packet" discussion for context.