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Subject: Re: [PATCH 1/2] drm/bridge: dw-hdmi: Add DT binding to disable
 hotplug detect
To:     Mykyta Poturai <ddone@aruko.org>
Cc:     Andrzej Hajda <a.hajda@samsung.com>,
        Laurent Pinchart <Laurent.pinchart@ideasonboard.com>,
        Jonas Karlman <jonas@kwiboo.se>,
        Jernej Skrabec <jernej.skrabec@siol.net>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        Sam Ravnborg <sam@ravnborg.org>,
        Boris Brezillon <boris.brezillon@collabora.com>,
        Liu Ying <victor.liu@nxp.com>, dri-devel@lists.freedesktop.org,
        linux-kernel@vger.kernel.org
References: <20210131095537.962292-1-ddone@aruko.org>
From:   Neil Armstrong <narmstrong@baylibre.com>
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Organization: Baylibre
Message-ID: <6b8c11e3-655d-9bd3-c8dd-8b2b0ea71954@baylibre.com>
Date:   Mon, 8 Feb 2021 10:19:43 +0100
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On 31/01/2021 10:55, Mykyta Poturai wrote:
> Add "disable-hpd" boolean binding for the device tree. When this option
> is turned on HPD-related IRQ is disabled and it is assumed that the HDMI
> connector is connected all the time. This may be useful in systems where
> it is impossible or undesirable to connect the HPD pin, or the
> connection is broken.

DRM mode forcing exists for this reason.

You can even force an EDID to have a fixed mode.

Neil

> 
> Signed-off-by: Mykyta Poturai <ddone@aruko.org>
> ---
>  drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> index 0c79a9ba48bb..4ca0ac130beb 100644
> --- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> +++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> @@ -194,6 +194,7 @@ struct dw_hdmi {
>  	unsigned int audio_cts;
>  	unsigned int audio_n;
>  	bool audio_enable;
> +	bool disable_hpd;
>  
>  	unsigned int reg_shift;
>  	struct regmap *regm;
> @@ -1559,7 +1560,7 @@ static void dw_hdmi_phy_disable(struct dw_hdmi *hdmi, void *data)
>  enum drm_connector_status dw_hdmi_phy_read_hpd(struct dw_hdmi *hdmi,
>  					       void *data)
>  {
> -	return hdmi_readb(hdmi, HDMI_PHY_STAT0) & HDMI_PHY_HPD ?
> +	return hdmi_readb(hdmi, HDMI_PHY_STAT0) & HDMI_PHY_HPD || hdmi->disable_hpd ?
>  		connector_status_connected : connector_status_disconnected;
>  }
>  EXPORT_SYMBOL_GPL(dw_hdmi_phy_read_hpd);
> @@ -1585,6 +1586,10 @@ void dw_hdmi_phy_setup_hpd(struct dw_hdmi *hdmi, void *data)
>  	 * Configure the PHY RX SENSE and HPD interrupts polarities and clear
>  	 * any pending interrupt.
>  	 */
> +
> +	if (hdmi->disable_hpd)
> +		return;
> +
>  	hdmi_writeb(hdmi, HDMI_PHY_HPD | HDMI_PHY_RX_SENSE, HDMI_PHY_POL0);
>  	hdmi_writeb(hdmi, HDMI_IH_PHY_STAT0_HPD | HDMI_IH_PHY_STAT0_RX_SENSE,
>  		    HDMI_IH_PHY_STAT0);
> @@ -3212,6 +3217,10 @@ struct dw_hdmi *dw_hdmi_probe(struct platform_device *pdev,
>  	mutex_init(&hdmi->cec_notifier_mutex);
>  	spin_lock_init(&hdmi->audio_lock);
>  
> +	if (of_property_read_bool(np, "disable-hpd")) {
> +		dev_info(hdmi->dev, "Disabling HPD\n");
> +		hdmi->disable_hpd = true;
> +	}
>  	ddc_node = of_parse_phandle(np, "ddc-i2c-bus", 0);
>  	if (ddc_node) {
>  		hdmi->ddc = of_get_i2c_adapter_by_node(ddc_node);
>