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

[Hans de Goede <hdegoede@redhat.com>]

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 ?

> 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.

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%7C686ea1d3bc2b4c6fa92cd
>> 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",
>>>
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