linux-kernel - Re: [PATCH 1/3] drm/bridge: dw-hdmi-qp: Return 0 in audio prepare when disconnected

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Message-ID: <8861545.DvuYhMxLoT@phil>
Date: Fri, 18 Jul 2025 09:43:26 +0200
From: Heiko Stuebner <heiko@...ech.de>
To: linux-kernel@...r.kernel.org,
 Detlev Casanova <detlev.casanova@...labora.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>,
 Liam Girdwood <lgirdwood@...il.com>, Mark Brown <broonie@...nel.org>,
 Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>,
 Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>,
 Detlev Casanova <detlev.casanova@...labora.com>,
 Douglas Anderson <dianders@...omium.org>,
 Sugar Zhang <sugar.zhang@...k-chips.com>,
 Cristian Ciocaltea <cristian.ciocaltea@...labora.com>,
 Charles Keepax <ckeepax@...nsource.cirrus.com>,
 Raag Jadav <raag.jadav@...el.com>, dri-devel@...ts.freedesktop.org,
 linux-sound@...r.kernel.org, kernel@...labora.com
Subject:
 Re: [PATCH 1/3] drm/bridge: dw-hdmi-qp: Return 0 in audio prepare when
 disconnected

Am Donnerstag, 17. Juli 2025, 23:56:18 Mitteleuropäische Sommerzeit schrieb Detlev Casanova:
> To configure audio registers, the clock of the video port in use must be
> enabled.
> As those clocks are managed by the VOP driver, they can't be enabled here
> to write the registers even when the HDMI cable is disconnected.
> 
> Furthermore, the registers values are computed from the TMDS char rate,
> which is not available when disconnected.
> 
> Returning -ENODEV seemed reasonable at first, but ASoC will log an error
> multiple times if dw_hdmi_qp_audio_prepare() return an error.
> Userspace might also retry multiple times, filling the kernel log with:
> 
> hdmi-audio-codec hdmi-audio-codec.0.auto: ASoC error (-19): at snd_soc_dai_prepare() on i2s-hifi
> 
> This has become even worse with the support of the second HDMI TX port.
> 
> Activating the clocks to write fake data (fake because the TMDS char
> rate is unavailable) would require API changes to communicate between
> VOP and HDMI, which doesn't really make sense.
> 
> Using a cached regmap to be dumped when a cable is connected won't work
> because writing order is important and some data needs to be retrieved
> from registers to write others.
> 
> Returning 0 to silently fail sounds like the best and simplest solution.
> 
> Signed-off-by: Detlev Casanova <detlev.casanova@...labora.com>
> ---
>  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 5e5f8c2f95be1..7d3d7b5084c8d 100644
> --- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi-qp.c
> +++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi-qp.c
> @@ -459,7 +459,7 @@ static int dw_hdmi_qp_audio_prepare(struct drm_connector *connector,
>  	bool ref2stream = false;
>  
>  	if (!hdmi->tmds_char_rate)
> -		return -ENODEV;
> +		return 0;

nit: part of me would like a short comment stating the requirment of the
running video-clock.

Heiko

>  
>  	if (fmt->bit_clk_provider | fmt->frame_clk_provider) {
>  		dev_err(hdmi->dev, "unsupported clock settings\n");
>