Re: [PATCH v2 17/29] drm: bridge: dw-hdmi: Refactor PHY power handling

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Jose,

On Thursday 05 Jan 2017 15:06:49 Jose Abreu wrote:
> On 05-01-2017 12:29, Laurent Pinchart wrote:
> > On Tuesday 20 Dec 2016 12:17:23 Jose Abreu wrote:
> >> On 20-12-2016 11:45, Russell King - ARM Linux wrote:
> >>> On Tue, Dec 20, 2016 at 03:33:48AM +0200, Laurent Pinchart wrote:
> >>>> Instead of spreading version-dependent PHY power handling code around,
> >>>> group it in two functions to power the PHY on and off and use them
> >>>> through the driver.
> >>>> 
> >>>> Powering off the PHY at the beginning of the setup phase is currently
> >>>> split in two locations for first and second generation PHYs, group all
> >>>> the operations in the dw_hdmi_phy_init() function.
> >>> 
> >>> This changes the behaviour of the driver.
> >>> 
> >>>> +static void dw_hdmi_phy_power_off(struct dw_hdmi *hdmi)
> >>>> +{
> >>>> +	if (hdmi->phy->gen == 1) {
> >>>> +		dw_hdmi_phy_enable_tmds(hdmi, 0);
> >>>> +		dw_hdmi_phy_enable_powerdown(hdmi, true);
> >>>> +	} else {
> >>>> +		dw_hdmi_phy_gen2_txpwron(hdmi, 0);
> >>>> +		dw_hdmi_phy_gen2_pddq(hdmi, 1);
> >>>> +	}
> >>>> +}
> >>>> @@ -1290,9 +1302,7 @@ static void dw_hdmi_phy_disable(struct dw_hdmi
> >>>> *hdmi)
> >>>>  	if (!hdmi->phy_enabled)
> >>>>  		return;
> >>>> 
> >>>> -	dw_hdmi_phy_enable_tmds(hdmi, 0);
> >>>> -	dw_hdmi_phy_enable_powerdown(hdmi, true);
> >>>> -
> >>>> +	dw_hdmi_phy_power_off(hdmi);
> >>> 
> >>> This makes dw_hdmi_phy_disable() power down a gen2 phy.
> >>> 
> >>> The iMX6 has a DW_HDMI_PHY_DWC_HDMI_3D_TX_PHY phy, which you list as a
> >>> gen2 phy.  I've been carrying this change for a while, which I've had
> >>> to revert (and finally expunge), as it causes problems on iMX6:
> >>> 
> >>> @@ -1112,6 +1112,14 @@ static void dw_hdmi_phy_disable(struct dw_hdmi
> >>> *hdmi)
> >>>         if (!hdmi->phy_enabled)
> >>>                 return;
> >>> 
> >>> +       /* Actually set the phy into low power mode */
> >>> +       dw_hdmi_phy_gen2_txpwron(hdmi, 0);
> >>> +
> >>> +       /* FIXME: We should wait for TX_READY to be deasserted */
> >>> +
> >>> +       dw_hdmi_phy_gen2_pddq(hdmi, 1);
> >>> +
> >>> +       /* This appears to have no effect on iMX6 */
> >>>         dw_hdmi_phy_enable_tmds(hdmi, 0);
> >>>         dw_hdmi_phy_enable_powerdown(hdmi, true);
> >>> 
> >>> So, I think your change here will cause problems for iMX6.
> >>> 
> >>> From what I remember, it seems that iMX6 has issues with RXSENSE/HPD
> >>> bouncing when the PHY is powered down.  I can't promise when I'll be
> >>> able to check for that again.
> >> 
> >> Indeed TX_READY must be low before asserting pddq.
> > 
> > The TX_READY signal is documented in the i.MX6 datasheet as being a PHY
> > output signal, but there seems to be no HDMI TX register from which its
> > state can be read. Do I need to poll the HDMI_PHY_PTRPT_ENBL register
> > through I2C ? How long is the PHY expected to take to set TX_READY to 0 ?
> 
> TX_READY can be read from register 0x1A of phy, BIT(2) (through
> I2C). Not sure if same offset for all phys though.

I have been told that another option is to poll the TX_PHY_LOCK bit in the 
phy_stat0 register. That would be a simpler solution that doesn't require I2C 
access. Could you confirm (or disconfirm) this ?

> >> HPD and RXSENSE should work in power down mode by enabling enhpdrxsense
> >> bit in phy_conf0 BUT to enter power down you must disable TX_PWRON,
> >> enhpdrxsense and enable PDDQ and PHY_RESET. Only after doing this (and
> >> consequently entering power down mode) you can enable again enhpdrxsense.
> > 
> > Thanks, I'll give it a try.

-- 
Regards,

Laurent Pinchart