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

[Jose Abreu]

Hi Laurent,


On 01-03-2017 11:09, Laurent Pinchart wrote:
> 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 ?

Yes (In our implementation we have TX_PHY_LOCK wired up to
TX_READY that comes from phy. But if using a custom phy or an
unusual implementation then this may not hold).

Best regards,
Jose Miguel Abreu

>>>> 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.