Hi, Pavel Machek <pavel@xxxxxx> writes: >> >>> +#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. > 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. > N900 will simply not charge from .5A. it used to with original maemo userspace/kernel. >> 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 ? -- balbi
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