linux-kernel - Re: [PATCH RESEND v3 1/5] drm/bridge: it6505: fix link training state HW register reset

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Message-ID: <4r5c5tbedw2hnkyqybcaxrjcc7lrdgxdbuhkzdvevdv6kmrxlw@5hb2aw6h4row>
Date: Tue, 16 Sep 2025 13:40:25 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Hermes.wu@....com.tw
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>,
        David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
        Pet.Weng@....com.tw, Kenneth.Hung@....com.tw, treapking@...omium.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RESEND v3 1/5] drm/bridge: it6505: fix link training
 state HW register reset

On Tue, Sep 16, 2025 at 12:47:41PM +0800, Hermes Wu via B4 Relay wrote:
> From: Hermes Wu <Hermes.wu@....com.tw>
> 
> When connect to a DP-to-HDMI device which does not connect
> to HDMI sink, it will report DPCD 00200h with SINK_COUNT = "0",
> and issue HPD_IRQ when SINK_COUNT change to "1".
> 
> IT6505 can not recive HPD_IRQ before training done and driver will
> force HW enter training done state when connect to such devices.
> 
> When HW is force to training done state and restart link training,
> bits FORCE_RETRAIN and MANUAL_TRAIN at REG_TRAIN_CTRL1 must be set
> at the same time to reset HW state.
> 
> Signed-off-by: Hermes Wu <Hermes.wu@....com.tw>
> ---
>  drivers/gpu/drm/bridge/ite-it6505.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 

Fixes: b5c84a9edcd4 ("drm/bridge: add it6505 driver")

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>


-- 
With best wishes
Dmitry