PROBLEM: Asus C201 video mode problems on HDMI hotplug (regression)

[Laurent Pinchart]

Hi Nick,

On Friday, 1 December 2017 02:11:46 EET Nick Bowler wrote:
> On 2017-11-27 22:30 -0500, Nick Bowler wrote:
> > A note about the test setup: I had to remove the test equipment so I
> > no longer have any information about the video mode from the sink side
> > (like in the photos).  Thus, with the current setup, I am using the
> > presense or absense of audio to determine whether the issue is present
> > or not.
> > 
> > The test procedure is: boot up, start music, then hotplug the hdmi four
> > times.  If sound is heard after all four connections, PASS; otherwise
> > FAIL.
> > 
> >  - I retested on 4.15-rc1 to confirm that the issue is still present (it
> >  is).
> >  
> >  - I applied the functional revert from earlier on top of 4.15-rc1 and the
> >    problem is fixed.
> >  
> >  - Returning to 4.15-rc1 and applying [Laurent Pinchart's] patch --
> >    the issue is present again (no change in behaviour compared to
> >    4.15-rc1).
> 
> Another data point... the following patch appears sufficient to restore
> working behaviour.
> 
> Cheers,
>   Nick
> 
> ---
>  drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 17 -----------------
>  1 file changed, 17 deletions(-)
> 
> diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c index
> bf14214fa464..3118fbd8433d 100644
> --- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> +++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> @@ -1101,8 +1101,6 @@ static void dw_hdmi_phy_power_off(struct dw_hdmi
> *hdmi) static int dw_hdmi_phy_power_on(struct dw_hdmi *hdmi)
>  {
>  	const struct dw_hdmi_phy_data *phy = hdmi->phy.data;
> -	unsigned int i;
> -	u8 val;
> 
>  	if (phy->gen == 1) {
>  		dw_hdmi_phy_enable_powerdown(hdmi, false);
> @@ -1116,21 +1114,6 @@ static int dw_hdmi_phy_power_on(struct dw_hdmi *hdmi)
> dw_hdmi_phy_gen2_txpwron(hdmi, 1);
>  	dw_hdmi_phy_gen2_pddq(hdmi, 0);
> 
> -	/* Wait for PHY PLL lock */
> -	for (i = 0; i < 5; ++i) {
> -		val = hdmi_readb(hdmi, HDMI_PHY_STAT0) & HDMI_PHY_TX_PHY_LOCK;
> -		if (val)
> -			break;
> -
> -		usleep_range(1000, 2000);
> -	}
> -
> -	if (!val) {
> -		dev_err(hdmi->dev, "PHY PLL failed to lock\n");
> -		return -ETIMEDOUT;
> -	}
> -
> -	dev_dbg(hdmi->dev, "PHY PLL locked %u iterations\n", i);

As you reported that the PLL lock failure message is not printed, the failure 
can only come from either the extra delay introduced by the above loop, or 
from reading the HDMI_PHY_STAT0 register.

How many iterations of the for loop execute before the condition becomes true 
?

>  	return 0;
>  }

-- 
Regards,

Laurent Pinchart