Hi, NeilBrown <nfbrown@xxxxxxxxxx> writes: > Firstly, you have made the current limit associated with each cable type > configurable (__usb_charger_set_cur_limit_by_type). This is nonsense. > The standard (e.g. BC-1.2) declares what the current limits are. There > is no reason for those not to be hard coded. I had raised the same concern WRT configuration current limits. > Secondly, you treat each charger type as having a single "cur_limit" and > utilize that limit by telling the PMIC to draw that much current. > Again, this is inconsistent with the specification. > BC-1.2 defines, for each charger type, a minimum and maximum current > level. > The minimum should always be available. Attempting to draw more than > that (but less that the max) might work or might cause the charger > to shut down, but you can be sure that the charger will respond to the > increased load by first reducing the voltage, and will not shut down > until the voltage has dropped below 2V. > If you try to draw more current than the maximum, then the charger might > shut down before the voltage drops below 2V. Very well put :-) > Given this understanding of the current available from the charger, > there are two approaches the PMIC might take. > 1/ if the PMIC is able to exercise fine control over the current it > draws, and if it can monitor the voltage on the charger, then it > could gradually increase the power being requested until the voltage > drops below some threshold (e.g. 4.75V), and then (probably) back off > a little. It should only increase at most up to the maximum, even if > the voltage remains high. It should probably start at zero rather > than at the minimum. This allows for lossage elsewhere. That's what most charging control SW I've seen in the past ends up doing. Correct > 2/ If the PMIC cannot measure voltage, or doesn't have sufficiently fine > control of the current requested, then it should request only the > minimum available current. Any more is not safe. correct -- balbi
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