[RFC] usb: typec: tcpm: remove operating_snk_mw for rdo

[Jun Li <jun.li@nxp.com>]

> -----Original Message-----
> From: Hans de Goede [mailto:hdegoede@redhat.com]
> Sent: 2018年4月20日 17:21
> To: Jun Li <jun.li@nxp.com>; linux@roeck-us.net;
> heikki.krogerus@linux.intel.com
> Cc: gregkh@linuxfoundation.org; linux-usb@vger.kernel.org; dl-linux-imx
> <linux-imx@nxp.com>
> Subject: Re: [PATCH RFC] usb: typec: tcpm: remove operating_snk_mw for rdo
> 
> Hi,
> 
> On 20-04-18 11:18, Jun Li wrote:
> >
> >> -----Original Message-----
> >> From: Hans de Goede [mailto:hdegoede@redhat.com]
> >> Sent: 2018年4月18日 19:40
> >> To: Jun Li <jun.li@nxp.com>; linux@roeck-us.net;
> >> heikki.krogerus@linux.intel.com
> >> Cc: gregkh@linuxfoundation.org; linux-usb@vger.kernel.org;
> >> dl-linux-imx <linux-imx@nxp.com>
> >> Subject: Re: [PATCH RFC] usb: typec: tcpm: remove operating_snk_mw
> >> for rdo
> >>
> >> Hi,
> >>
> >> On 17-04-18 08:01, Li Jun wrote:
> >>> This patch is a further update for rdo based on [1], which removed
> >>> max_snk_ma/mv/mw but kept operating_snk_mw.
> >>> operating_snk_mw is only used to judge capability mismatch, per PD
> >>> spec, we can achieve this via compare the selected source PDO and
> >>> matching sink PDO, also after patch [1], we don't limit the PDO
> >>> matching between the same type, so the rdo operating and max
> >>> current/power calculation should be updated accordingly.
> >>
> >> I do not believe that this is correct, lets take a device with a
> >> fusb302 tcpc with the following PDO-s:
> >>
> >> 	PDO_FIXED(5000, 400, PDO_FIXED_FLAGS)
> >> 	PDO_VAR(5000, 12000, 3000);
> >>
> >> And an operating_snk_mw of 2500mW then according to your new code a
> >> charger which supplies 12V 2A will now get the mismatch bit set even
> >> though it is delivering 24W.
> >>
> >
> > Per PD spec, my understanding is to judge capability mismatch, we
> > should use *max* current/power, not this operating power.
> 
> Ok, I'm not familiar with the PD spec, perhaps someone who knows it well can
> comment here ?

Hi Guenter,
Could you please comment here?

Thanks
Jun

> 
> > In your case(VAR PDO), the max current is 3000mA, can I say the max
> > power is 3000mA * 5V = 15W? so the max current required at 12V is 15W
> > / 12V = 1.25A, so yes, the 12V@2A is enough, do you think this kind of
> > calculation is reasonable?
> 
> That does not sound unreasonable, the real question is when exactly should we
> set the capability mismatch bit, once we have that more clear how to
> implement this should become clear too.

Fully agree, below is the capability mismatch bit related description from PD spec:

"If the Capability Mismatch bit is set to one
The Maximum Operating Current/Power field may contain a value larger than
the maximum current/power offered in the Source_Capabilities Message’s PDO
as referenced by the Object position field. This enables the Sink to indicate that
it requires more current/power than is being offered. If the Sink requires a
different voltage this will be indicated by its Sink_Capabilities Message."

"6.4.2.8 Maximum Operating Current
The Maximum Operating Current field in the Request Message shall be set to
the highest current the Sink will ever require. The difference between
the Operating Current and Maximum Operating Current fields
(when the GiveBack Flag is cleared) is used by the Device Policy Manager
in the Source to calculate the size of the Power Reserve to be maintained
(see Section 8.2.5.1). The Operating Current value shall be less than or
equal to the Maximum Operating Current value.
When the Capabilities Mismatch bit is set to zero the requested Maximum Operating
Current shall be less than or equal to the current in the offered Source Capabilities
since the Source will need to reserve this power for future use. ...
 
When the Capabilities Mismatch bit is set to one the requested Maximum
Operating Current may be greater than the current in the offered Source
Capabilities since the Source will need this information to ascertain
the Sink’s actual needs".

> 
> Regards,
> 
> Hans
> 
> 
> 
> >
> >> I really don't see any way to fix this and I believe we should just
> >> keep the operating_snk_mw field.
> >
> > I had the same worry of breaking existing users, but found there is
> > something not matching PD spec, so want to get comments, if we really
> > need another input (beside sink PDO) in practice, we can keep it.
> >
> > Thanks
> > Jun
> >>
> >> Regards
> >>
> >> Hans
> >>
> >>
> >>
> >>> [1]https://emea01.safelinks.protection.outlook.com/?url=https%3A%2F%
> >>> 2F
> >>>
> >>
> patchwork.kernel.org%2Fpatch%2F10342299%2F&data=02%7C01%7Cjun.li%4
> >> 0nxp
> >>> .com%7C796c943804cc4a333a7c08d5a5212e41%7C686ea1d3bc2b4c6fa9
> 2cd
> >> 99c5c30
> >>>
> >>
> 1635%7C0%7C0%7C636596484284807487&sdata=BH74zzVppAi7Fa8jtRt2cwc
> >> d%2F%2F
> >>> o6idNC5hk5zyoWIA4%3D&reserved=0
> >>>
> >>> Signed-off-by: Li Jun <jun.li@nxp.com>
> >>> ---
> >>>    drivers/usb/typec/tcpm.c | 52
> >> ++++++++++++++++++++++++++++++------------------
> >>>    1 file changed, 33 insertions(+), 19 deletions(-)
> >>>
> >>> diff --git a/drivers/usb/typec/tcpm.c b/drivers/usb/typec/tcpm.c
> >>> index
> >>> 27192083..0be04b3 100644
> >>> --- a/drivers/usb/typec/tcpm.c
> >>> +++ b/drivers/usb/typec/tcpm.c
> >>> @@ -1854,28 +1854,42 @@ static int tcpm_pd_build_request(struct
> >> tcpm_port *port, u32 *rdo)
> >>>    	else
> >>>    		mv = pdo_min_voltage(pdo);
> >>>
> >>> -	/* Select maximum available current within the sink pdo's limit */
> >>> -	if (type == PDO_TYPE_BATT) {
> >>> -		mw = min_power(pdo, matching_snk_pdo);
> >>> -		ma = 1000 * mw / mv;
> >>> -	} else {
> >>> -		ma = min_current(pdo, matching_snk_pdo);
> >>> -		mw = ma * mv / 1000;
> >>> -	}
> >>> -
> >>>    	flags = RDO_USB_COMM | RDO_NO_SUSPEND;
> >>>
> >>> -	/* Set mismatch bit if offered power is less than operating power */
> >>> -	max_ma = ma;
> >>> -	max_mw = mw;
> >>> -	if (mw < port->operating_snk_mw) {
> >>> -		flags |= RDO_CAP_MISMATCH;
> >>> -		if (type == PDO_TYPE_BATT &&
> >>> -		    (pdo_max_power(matching_snk_pdo) >
> pdo_max_power(pdo)))
> >>> -			max_mw = pdo_max_power(matching_snk_pdo);
> >>> -		else if (pdo_max_current(matching_snk_pdo) >
> >>> -			 pdo_max_current(pdo))
> >>> +	switch (type) {
> >>> +	case PDO_TYPE_FIXED:
> >>> +	case PDO_TYPE_VAR:
> >>> +		if (pdo_type(matching_snk_pdo) == PDO_TYPE_BATT)
> >>> +			max_ma = pdo_max_power(matching_snk_pdo) * 1000 /
> mv;
> >>> +		else
> >>>    			max_ma = pdo_max_current(matching_snk_pdo);
> >>> +
> >>> +		if (max_ma > pdo_max_current(pdo)) {
> >>> +			flags |= RDO_CAP_MISMATCH;
> >>> +			ma = pdo_max_current(pdo);
> >>> +		} else {
> >>> +			ma = max_ma;
> >>> +		}
> >>> +		break;
> >>> +	case PDO_TYPE_BATT:
> >>> +		if (pdo_type(matching_snk_pdo) == PDO_TYPE_BATT)
> >>> +			max_mw = pdo_max_power(matching_snk_pdo);
> >>> +		else
> >>> +			max_mw = pdo_max_current(matching_snk_pdo) *
> >>> +				 pdo_min_voltage(matching_snk_pdo) /
> >>> +				 1000;
> >>> +
> >>> +		if (max_mw > pdo_max_power(pdo)) {
> >>> +			flags |= RDO_CAP_MISMATCH;
> >>> +			mw = pdo_max_power(pdo);
> >>> +		} else {
> >>> +			mw = max_mw;
> >>> +		}
> >>> +
> >>> +		ma = mw * 1000 / mv;
> >>> +		break;
> >>> +	default:
> >>> +		break;
> >>>    	}
> >>>
> >>>    	tcpm_log(port, "cc=%d cc1=%d cc2=%d vbus=%d vconn=%s
> >> polarity=%d",
> >>>