Hi! > >> >>> +#define DEFAULT_SDP_CUR_LIMIT (500 - DEFAULT_CUR_PROTECT) > >> >> > >> >> According to the spec we should always be talking about unit loads (1 > >> >> unit load is 100mA for HS/FS/LS and 150mA for SS). Also, this will not > >> >> work for SS capable ports and SS gadgets (we have quite a few of them, > >> >> actually). You're missing the opportunity of charging at 900mA. > >> > > >> > I follow the DCP/SDP/CDP/ACA type's default current limitation and > >> > user can set them what they want. > >> > >> no, the user CANNOT set it to what they want. If you get enumerated > >> @100mA and the user just decides to set it to 2000mA, s/he could even > >> melt the USB connector. The kernel _must_ prevent such cases. > > > > root should be allowed to do that. > > root should not be allowed to put user at risk. The usb connector is a > path to earth ground in most (all?) desktop computers. Allowing root to > put that connector in a situation where it could melt the connector and > short mains should never be allowed. Be sure that hardware people put reasonable precautions... > > Very often, you want to charge using 1.8A from an old desktop PC. > > if that old desktop's port is not a charging port, you shouldn't be > allowed to do that. Not ever. Yes, Felipe just decided that I should not be able to charge my N900 in useful way. > > N900 will simply not charge from .5A. > > it used to with original maemo userspace/kernel. Yeah, at about 10% per night. > >> a) you are connected to a dedicated charger > >> > >> In this case, you can get up to 2000mA depending on the charger. > >> > >> If $this charger can give you or not 2000mA is not detectable, > >> so what do charging ICs do ? They slowly increase the attached > >> load accross VBUS/GND and measure VBUS value. When IC notices > >> VBUS dropping bit, step back to previous load. > >> > >> This means you will always charger with maximum rating of DCP. > >> > >> Why would user change this ? More is unsafe, less is just > >> stupid. > > > > Actually, less is not stupid. Charging li-ion battery from li-ion battery might > > be stupid. Imagine I'm on train, with device like N900 (50% battery) and power bank > > (3Ah). I'm actively using the device. If I let it charge at full current, I'll waste > > energy. If I limit current to approximately the power consumption, it will run the > > powerbank empty, first, then empty the internal battery, maximizing total time I > > can use the device. > > why would you waste energy ? What the charger chip would do is charge > battery to maximum then just to maintenance charge from that point > on. Where is energy being wasted other than normal heat dissipation ? Physics 101, of course wasted energy goes to heat. Lets not waste energy by charging li-ion from li-ion when it is not required. Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
