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

[Maxime Ripard <mripard@kernel.org>]

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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@60Hz 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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