linux-kernel - Re: [PATCH] drm/bridge: ite-it6263: Support HDMI vendor specific infoframe

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Message-ID: <jaqzhm6oi6emkpqrysdgxppfndge46x5hsarczplboyfaw7p26@o5nr7xvtrxp4>
Date: Fri, 5 Sep 2025 17:31:02 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Liu Ying <victor.liu@....com>
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>,
        Dmitry Baryshkov <lumag@...nel.org>, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/bridge: ite-it6263: Support HDMI vendor specific
 infoframe

On Fri, Sep 05, 2025 at 01:46:56PM +0800, Liu Ying wrote:
> On 09/05/2025, Dmitry Baryshkov wrote:
> > On Thu, Sep 04, 2025 at 05:10:02PM +0800, Liu Ying wrote:
> >> IT6263 supports HDMI vendor specific infoframe.  The infoframe header
> >> and payload are configurable via NULL packet registers.  The infoframe
> >> is enabled and disabled via PKT_NULL_CTRL register.  Add the HDMI vendor
> >> specific infoframe support.
> >>
> >> Signed-off-by: Liu Ying <victor.liu@....com>
> >> ---
> >>  drivers/gpu/drm/bridge/ite-it6263.c | 72 ++++++++++++++++++++++++++-----------
> >>  1 file changed, 52 insertions(+), 20 deletions(-)
> >>
> >> +	case HDMI_INFOFRAME_TYPE_VENDOR:
> >> +		const char zero_bulk[HDMI_PKT_HB_PB_CHUNK_SIZE] = { };
> >> +
> >> +		/* clear NULL packet registers due to undefined default value */
> >> +		regmap_bulk_write(regmap, HDMI_REG_PKT_HB(0),
> >> +				  zero_bulk, sizeof(zero_bulk));
> > 
> > What if you move this to the probe function? Then there will be no need
> > to write those registers each time the infoframe is being written.
> 
> Good idea.  But looking at drm_hdmi_vendor_infoframe_from_display_mode(),
> hdmi_vendor_infoframe_length() and hdmi_vendor_infoframe_pack_only(), the
> payload length could be changed in runtime according to display mode's VIC
> and flags(see DRM_MODE_FLAG_3D_MASK).  And, IT6263 supports HDMI1.4a 3D
> formats according to it's product information[1].  So, it makes sense to
> clear HDMI_REG_PKT_PB(5) and HDMI_REG_PKT_PB(6) here which map to ptr[8]
> and ptr[9] in hdmi_vendor_infoframe_pack_only().  For v2, I'd move the
> NULL packet registers bulk write to it6263_hdmi_config()(i.e., it6263_probe())
> and write zero to HDMI_REG_PKT_PB(5) and HDMI_REG_PKT_PB(6) here.

Then you don't even need to write zeroes in probe(). Just write
something like:

regmap_bulk_write(regmap, HDMI_REG_PKT_HB(len), zero_bulk, FRAMESIZE-len);

But as a note: I don't think other drivers zero out packet memory. I
think it's expected that displays ignore the frame after the 'len'
bytes.

> 
> What do you think?
> 
> [1] www.ite.com.tw/en/product/cate1/IT6263
> 
> > 
> > LGTM otherwise.
> > 
> >> +
> >> +		/* write header and payload */
> >> +		regmap_bulk_write(regmap, HDMI_REG_PKT_HB(0), buffer, len);
> >> +
> >> +		regmap_write(regmap, HDMI_REG_PKT_NULL_CTRL,
> >> +			     ENABLE_PKT | REPEAT_PKT);
> >> +		break;
> > 
> 
> -- 
> Regards,
> Liu Ying

-- 
With best wishes
Dmitry