linux-kernel - Re: [PATCH v6 03/12] drm/bridge: cdns-dsi: Fix phy de-init and flag it so

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Message-ID: <dqmzdxhgnabfq6zzbd424ajfd734gza5aitmk5bfswff52d76r@2swxl627az3d>
Date: Mon, 13 Jan 2025 11:40:03 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Aradhya Bhatia <aradhya.bhatia@...ux.dev>
Cc: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>, 
	Laurent Pinchart <laurent.pinchart@...asonboard.com>, Andrzej Hajda <andrzej.hajda@...el.com>, 
	Neil Armstrong <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>, 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>, 
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, Nishanth Menon <nm@...com>, 
	Vignesh Raghavendra <vigneshr@...com>, Devarsh Thakkar <devarsht@...com>, 
	Praneeth Bajjuri <praneeth@...com>, Udit Kumar <u-kumar1@...com>, 
	Jayesh Choudhary <j-choudhary@...com>, DRI Development List <dri-devel@...ts.freedesktop.org>, 
	Linux Kernel List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 03/12] drm/bridge: cdns-dsi: Fix phy de-init and flag
 it so

On Sun, Jan 12, 2025 at 12:57:29AM +0530, Aradhya Bhatia wrote:
> From: Aradhya Bhatia <a-bhatia1@...com>
> 
> The driver code doesn't have a de-initialization path as yet, and so it
> does not clear the phy_initialized flag while suspending. This is a
> problem because after resume the driver looks at this flag to determine
> if a Phy re-initialization is required or not. It is in fact required
> because the hardware is resuming from a suspend, but the driver does not
> carry out any re-initialization causing the D-Phy to not work at all.
> 
> Add the counterpart of phy_power_on(), that is phy_power_off() from the
> _bridge_disable() and clear the flags so that the Phy can be initialized
> again when required.
> 
> Move the Phy initialization from _bridge_enable() to _resume(), and
> de-initialize during the _suspend() - so that the phy_{init, exit}()
> take place once every resume/suspend cycle.

Is it okay to call phy_init() before writing MCTL_DPHY_CFG0 ?

> 
> The order of calls still remains the same. phy_init() needs to be called
> before phy_power_on() - which happens still. What this patch changes is
> the frequency of the phy_init() call. Instead of it being called once
> every bridge enable/disable cycle, it is now being called once every
> resume/suspend cycle. This move has been considered safe after numerous
> tests with the hardware.
> 
> Fixes: fced5a364dee ("drm/bridge: cdns: Convert to phy framework")
> Signed-off-by: Aradhya Bhatia <a-bhatia1@...com>
> Signed-off-by: Aradhya Bhatia <aradhya.bhatia@...ux.dev>
> ---
>  drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)

-- 
With best wishes
Dmitry