Re: [PATCH v1] drm/bridge: ti-sn65dsi86: Transition to LP mode on every video line

[Emanuele Ghidoli <ghidoliemanuele@gmail.com>]

On 16/09/2025 16:45, Doug Anderson wrote:
> Hi,
> 
> On Tue, Sep 16, 2025 at 7:22 AM Emanuele Ghidoli
> <ghidoliemanuele@gmail.com> wrote:
>>
>> From: Emanuele Ghidoli <emanuele.ghidoli@toradex.com>
>>
>> The component datasheet recommends, to reduce power consumption,
>> transitioning to LP mode on every video line.
>>
>> Enable the MIPI_DSI_MODE_VIDEO_NO_HFP and MIPI_DSI_MODE_VIDEO_NO_HBP
>> flags so that the bridge can enter LP mode during the horizontal front
>> porch and back porch periods.
>>
>> Signed-off-by: Emanuele Ghidoli <emanuele.ghidoli@toradex.com>
>> ---
>> Cc: Douglas Anderson <dianders@chromium.org>
>> Cc: Andrzej Hajda <andrzej.hajda@intel.com>
>> Cc: Neil Armstrong <neil.armstrong@linaro.org>
>> Cc: Robert Foss <rfoss@kernel.org>
>> Cc: Laurent Pinchart <Laurent.pinchart@ideasonboard.com>
>> Cc: Jonas Karlman <jonas@kwiboo.se>
>> Cc: Jernej Skrabec <jernej.skrabec@gmail.com>
>> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
>> Cc: Maxime Ripard <mripard@kernel.org>
>> Cc: Thomas Zimmermann <tzimmermann@suse.de>
>> Cc: David Airlie <airlied@gmail.com>
>> Cc: Simona Vetter <simona@ffwll.ch>
>> Cc: Jayesh Choudhary <j-choudhary@ti.com>
>> Cc: <dri-devel@lists.freedesktop.org>
>> Cc: <linux-kernel@vger.kernel.org>
>> ---
>>  drivers/gpu/drm/bridge/ti-sn65dsi86.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> I put this on a sc7180-trogdor based Chromebook and the display no
> longer comes up. I don't personally know the MIPI side of the spec too
> well so I have no idea why that would be.
> 
> -Doug

Hi Doug,
thanks for the test.
According to the datasheet, LP is recommended for the front porch and optional
for the back porch.
Could you please run another test by keeping only MIPI_DSI_MODE_VIDEO_NO_HFP
and removing MIPI_DSI_MODE_VIDEO_NO_HBP?

dsi->mode_flags = MIPI_DSI_MODE_VIDEO | MIPI_DSI_MODE_VIDEO_NO_HFP;

Kind regards,
Emanuele