linux-kernel - Re: [PATCH] drm/bridge: dw-hdmi-qp: fix multi-channel audio output

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Message-ID: <13d33158-b814-4ac1-b8de-ec30ff16c783@collabora.com>
Date: Tue, 20 Jan 2026 14:52:35 +0200
From: Cristian Ciocaltea <cristian.ciocaltea@...labora.com>
To: Christian Hewitt <christianshewitt@...il.com>,
 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 <dmitry.baryshkov@....qualcomm.com>,
 Detlev Casanova <detlev.casanova@...labora.com>,
 Douglas Anderson <dianders@...omium.org>, Andy Yan
 <andy.yan@...k-chips.com>, Sugar Zhang <sugar.zhang@...k-chips.com>,
 Luca Ceresoli <luca.ceresoli@...tlin.com>, Heiko Stuebner <heiko@...ech.de>,
 dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/bridge: dw-hdmi-qp: fix multi-channel audio output

Hi Christian,

On 12/6/25 9:27 AM, Christian Hewitt wrote:
> From: Jonas Karlman <jonas@...boo.se>
> 
> Channel Allocation (PB4) and Level Shift Information (PB5) are
> configured with values from PB1 and PB2 due to the wrong offset
> being used. This results in missing audio channels or incorrect
> speaker placement when playing multi-channel audio.
> 
> Use the correct offset to fix multi-channel audio output.
> 
> Fixes: fd0141d1a8a2 ("drm/bridge: synopsys: Add audio support for dw-hdmi-qp")
> Reported-by: Christian Hewitt <christianshewitt@...il.com>
> Signed-off-by: Jonas Karlman <jonas@...boo.se>
> 
> ---
> buffer is a pointer to u8 while data written to PKT_AUDI_CONTENTS
> is u32, so buffer contains audio infoframe header (buffer[0:2]) +
> checksum (buffer[3]) + payload byte 1-10 (buffer[4:13]), e.g.
> 
> regmap_bulk_write(hdmi->regm, PKT_AUDI_CONTENTS1, &buffer[3], 1)
> .. will write PB0-PB3 to AUDI_CONTENTS1
> 
> regmap_bulk_write(hdmi->regm, PKT_AUDI_CONTENTS2, &buffer[4], 1)
> .. will write PB1-PB4 to AUDI_CONTENTS2, but should be PB4-PB7
> 
> &buffer[4] will point to payload byte 4 not payload byte 1, due
> to u8/u32 and not considering the size of header+checksum (3+1).
> ---
>  drivers/gpu/drm/bridge/synopsys/dw-hdmi-qp.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi-qp.c b/drivers/gpu/drm/bridge/synopsys/dw-hdmi-qp.c
> index f3a13da488e6..7b8a69383dc4 100644
> --- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi-qp.c
> +++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi-qp.c
> @@ -845,7 +845,7 @@ static int dw_hdmi_qp_config_audio_infoframe(struct dw_hdmi_qp *hdmi,
>  
>  	regmap_bulk_write(hdmi->regm, PKT_AUDI_CONTENTS0, &header_bytes, 1);
>  	regmap_bulk_write(hdmi->regm, PKT_AUDI_CONTENTS1, &buffer[3], 1);
> -	regmap_bulk_write(hdmi->regm, PKT_AUDI_CONTENTS2, &buffer[4], 1);
> +	regmap_bulk_write(hdmi->regm, PKT_AUDI_CONTENTS2, &buffer[7], 1);

Since making use of regmap_bulk_write(), this could be further optimized as:

-       regmap_bulk_write(hdmi->regm, PKT_AUDI_CONTENTS1, &buffer[3], 1);
-       regmap_bulk_write(hdmi->regm, PKT_AUDI_CONTENTS2, &buffer[4], 1);
+       regmap_bulk_write(hdmi->regm, PKT_AUDI_CONTENTS1, &buffer[3], 2);

Regardless,

Reviewed-by: Cristian Ciocaltea <cristian.ciocaltea@...labora.com>

Please note you also need to provide your SoB, check "Sign your work ..."
section in [1].

Regards,
Cristian

[1] https://www.kernel.org/doc/Documentation/process/submitting-patches.rst