On 04/20/2018 03:51 AM, Jun Li wrote:
-----Original Message-----
From: Hans de Goede [mailto:hdegoede@xxxxxxxxxx]
Sent: 2018年4月20日 17:21
To: Jun Li <jun.li@xxxxxxx>; linux@xxxxxxxxxxxx;
heikki.krogerus@xxxxxxxxxxxxxxx
Cc: gregkh@xxxxxxxxxxxxxxxxxxx; linux-usb@xxxxxxxxxxxxxxx; dl-linux-imx
<linux-imx@xxxxxxx>
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@xxxxxxxxxx]
Sent: 2018年4月18日 19:40
To: Jun Li <jun.li@xxxxxxx>; linux@xxxxxxxxxxxx;
heikki.krogerus@xxxxxxxxxxxxxxx
Cc: gregkh@xxxxxxxxxxxxxxxxxxx; linux-usb@xxxxxxxxxxxxxxx;
dl-linux-imx <linux-imx@xxxxxxx>
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?
I am not, and never was, the kind of person who would blindly follow a specification.
I use specifications as guideline. For PD, when I implemented the code, I made sure
that the implementation worked with as many power adapters and dongles as I could get
my hand on.
At this point in time, I would only change the code myself if it is known to be broken.
Otherwise I would leave it alone. I would _never_ make a change because my interpretation
of the specification is different, unless I can prove that the current code is wrong and
causes problems.
Unfortunately, I don't currently have a setup to test the current version of the code,
nor the time to do all the testing. I am more and more concerned, though, that changes
are made out of principle, not because something has been shown to be broken. But that is
just a personal concern, and without re-testing everything I don't really have a strong
case for or against those changes.
Guenter
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@xxxxxxx>
---
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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