Hi Adam and Heikki, On Mon, Sep 13, 2021 at 03:15:46PM +0000, Adam Thomson wrote: > On 13 September 2021 14:30, Heikki Krogerus wrote: > > > > My plan is to register a separate power supply for each PDO. So for > > every source PDO and every sink PDO a port has in its capabilities, > > you'll have a separate power supply registered, and the same for the > > partner when it's connected. With every connection there should always > > be one active (online) source psy and active sink psy (if the port is > > source, one of the port's source psys will be active and the partner > > will have the active sink psy, or vise versa - depending on the role). > > > > Each PDO represents a "Power Supply" so to me that approach just > > makes the most sense. It will require a bit of work in kernel, however > > in user space it should mean that we only have a single new attribute > > file for the power supplies named "pdo" that returns a single PDO. > > > > Let me know if you guys see any obvious problems with the idea. > > Otherwise, that is how we really need to do this. That will make > > things much more clear in user space. I have a feeling it will make > > things easier in kernel as well in the long run. > > > > Adding Adam and Guenter. It would be good if you guys could comment > > the idea as well. > > Hi Heikki, > > Thanks for CCing me. My two pence worth is that I always envisaged the PSY > representation as being 1 PSY for 1 power source. I consider this in a > similar manner to the Regulator framework, where 1 regulator can support a range > of voltages and currents, but this is covered by 1 regulator instance as it's > just a single output. For USB-PD we have a number of options for voltage/current > combos, including PPS which is even lower granularity, but it's still only one > port. I get the feeling that having PSY instances for each and every PDO might > be a little confusing and these will never be concurrent. > > However, I'd be keen to understand further and see what restrictions/issues are > currently present as I probably don't have a complete view of this right now. I > wouldn't want to dismiss something out of turn, especially when you obviously > have good reason to suggest such an approach. I thought of one more potential downside to one-psy-per-pdo: Remember that a source or sink's Capabilities may dynamically change without a port disconnect, and this could make one-psy-per-pdo much more chatty with power supply deletions and re-registrations on load balancing events. At basically any time, a power source may send a new SRC_CAP to the sink which adjusts, deletes, or adds to the list of PDOs, without the connection state machine registering a disconnect. In a real world case, I have a charger in my kitchen that has 2 USB-C ports and supports a total of 30W output. When one device is plugged in: 5V 3A, 9V 3A, 15V 2A However, when two devices are plugged in, each sees: 5V 3A The load balancing event would result in two power supply deletions, whereas if it were a single psy per power supply (incorporating the list of PDO choices) it would just be a single PROP_CHANGED event. It seems cleaner to me to have deletions and additions only possible when the thing is unplugged or plugged. Thanks, Benson -- Benson Leung Staff Software Engineer Chrome OS Kernel Google Inc. bleung@xxxxxxxxxx Chromium OS Project bleung@xxxxxxxxxxxx
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