linux-kernel - Re: [PATCH] drm/bridge: it6505: Fix inverted reset polarity

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Message-ID: <5eic3qpeocp54my5clu3umigog6fe5zs5drpbyzpholmalcmcw@mh25vgvxd5tx>
Date: Thu, 31 Oct 2024 21:37:48 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Chen-Yu Tsai <wenst@...omium.org>
Cc: Andrzej Hajda <andrzej.hajda@...el.com>, 
	Neil Armstrong <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>, 
	Laurent Pinchart <Laurent.pinchart@...asonboard.com>, Jonas Karlman <jonas@...boo.se>, 
	Jernej Skrabec <jernej.skrabec@...il.com>, Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
	Matthias Brugger <matthias.bgg@...il.com>, 
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>, linux-mediatek@...ts.infradead.org, 
	linux-arm-kernel@...ts.infradead.org, stable@...r.kernel.org
Subject: Re: [PATCH] drm/bridge: it6505: Fix inverted reset polarity

On Tue, Oct 29, 2024 at 05:54:10PM +0800, Chen-Yu Tsai wrote:
> The IT6505 bridge chip has a active low reset line. Since it is a
> "reset" and not an "enable" line, the GPIO should be asserted to
> put it in reset and deasserted to bring it out of reset during
> the power on sequence.
> 
> The polarity was inverted when the driver was first introduced, likely
> because the device family that was targeted had an inverting level
> shifter on the reset line.
> 
> The MT8186 Corsola devices already have the IT6505 in their device tree,
> but the whole display pipeline is actually disabled and won't be enabled
> until some remaining issues are sorted out. The other known user is
> the MT8183 Kukui / Jacuzzi family; their device trees currently do not
> have the IT6505 included.
> 
> Fix the polarity in the driver while there are no actual users.
> 
> Fixes: b5c84a9edcd4 ("drm/bridge: add it6505 driver")
> Cc: <stable@...r.kernel.org>
> Signed-off-by: Chen-Yu Tsai <wenst@...omium.org>
> ---
>  drivers/gpu/drm/bridge/ite-it6505.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)

The datasheet describes the pin as Active LOW, so the change seems to be
correct.

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>

-- 
With best wishes
Dmitry