linux-kernel - Re: [PATCH v4 2/4] drm/bridge: synopsys: Add DW HDMI QP TX Controller support library

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Message-ID: <20240902-turtle-of-major-glory-efb4e8@houat>
Date: Mon, 2 Sep 2024 09:36:50 +0200
From: Maxime Ripard <mripard@...nel.org>
To: Cristian Ciocaltea <cristian.ciocaltea@...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>, 
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, 
	Daniel Vetter <daniel@...ll.ch>, Sandy Huang <hjc@...k-chips.com>, 
	Heiko Stübner <heiko@...ech.de>, Andy Yan <andy.yan@...k-chips.com>, 
	Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, 
	Conor Dooley <conor+dt@...nel.org>, Mark Yao <markyao0591@...il.com>, 
	Sascha Hauer <s.hauer@...gutronix.de>, dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, linux-rockchip@...ts.infradead.org, devicetree@...r.kernel.org, 
	kernel@...labora.com, Alexandre ARNOUD <aarnoud@...com>, 
	Luis de Arquer <ldearquer@...il.com>, Algea Cao <algea.cao@...k-chips.com>
Subject: Re: [PATCH v4 2/4] drm/bridge: synopsys: Add DW HDMI QP TX
 Controller support library

On Sat, Aug 31, 2024 at 01:21:48AM GMT, Cristian Ciocaltea wrote:
> On 8/27/24 11:58 AM, Maxime Ripard wrote:
> > On Mon, Aug 19, 2024 at 01:29:29AM GMT, Cristian Ciocaltea wrote:
> >> +static irqreturn_t dw_hdmi_qp_main_hardirq(int irq, void *dev_id)
> >> +{
> >> +	struct dw_hdmi_qp *hdmi = dev_id;
> >> +	struct dw_hdmi_qp_i2c *i2c = hdmi->i2c;
> >> +	u32 stat;
> >> +
> >> +	stat = dw_hdmi_qp_read(hdmi, MAINUNIT_1_INT_STATUS);
> >> +
> >> +	i2c->stat = stat & (I2CM_OP_DONE_IRQ | I2CM_READ_REQUEST_IRQ |
> >> +			    I2CM_NACK_RCVD_IRQ);
> >> +
> >> +	if (i2c->stat) {
> >> +		dw_hdmi_qp_write(hdmi, i2c->stat, MAINUNIT_1_INT_CLEAR);
> >> +		complete(&i2c->cmp);
> >> +	}
> >> +
> >> +	if (stat)
> >> +		return IRQ_HANDLED;
> >> +
> >> +	return IRQ_NONE;
> >> +}
> > 
> > If the scrambler is enabled, you need to deal with hotplug. On hotplug,
> > the monitor will drop its TMDS ratio and scrambling status, but the
> > driver will keep assuming it's been programmed.
> > 
> > If you don't have a way to deal with hotplug yet, then I'd suggest to
> > just drop the scrambler setup for now.
> 
> Thanks for the heads up!
> 
> HPD is partially handled by the RK platform driver, which makes use of
> drm_helper_hpd_irq_event(). Since the bridge sets DRM_BRIDGE_OP_DETECT
> flag, the dw_hdmi_qp_bridge_detect() callback gets executed, which in turn
> verifies the PHY status via ->read_hpd() implemented as
> dw_hdmi_qp_rk3588_read_hpd() in the platform driver.

It's not only about hotplug detection, it's also about what happens
after you've detected a disconnection / reconnection.

The framework expects to keep the current mode as is, despite the
monitor not being setup to use the scrambler anymore, and the display
remains black.

> During my testing so far it worked reliably when switching displays with
> different capabilities.  I don't have a 4K@...z display at the moment, but
> used the HDMI RX port on the Rock 5B board in a loopback connection to
> verify this mode, which triggered the high TMDS clock ratio and scrambling
> setup as well.

How did you test exactly?

Maxime

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