iPod Classic: initialize USB power configuration

This patch limits the drawn USB current to 100/500mA, instead of
the actual 200/1000mA settings. It also initializes other USB power
related GPIOs.

Solves some USB disconnect issues: FS#12990, FS#12956. I am using a
powered USB HUB with no problems (Vusb=5.05V unloaded), but there
are lots of USB disconnects when using the motherboard USB ports
(Vusb=4.91V), this patch solves all my issues.

Actually, it seems that the USB current drain is limited to 1000mA,
when a load peak occurs most USB2 ports deliver more than 500mA, as
current consumption increases the USB voltage decreases, an excesive
voltage drop produces USB disconnections. Limiting USB current drain
to 500mA also limits the voltage drop, preventing subsequent USB
failures.

Anyway, to minimize voltage drop, it is recommended to use quality
cables and preferably connect to USB ports with higher Vusb.

Change-Id: I1b931aa18ec93bfd1214e475a72e42893eff52f6

1 files changed, 38 insertions, 0 deletions

diff --git a/firmware/target/arm/s5l8702/ipod6g/power-ipod6g.c b/firmware/target/arm/s5l8702/ipod6g/power-ipod6g.c
index 2e0fe87883..50e91b616e 100644
--- a/firmware/target/arm/s5l8702/ipod6g/power-ipod6g.c
+++ b/firmware/target/arm/s5l8702/ipod6g/power-ipod6g.c
@@ -43,6 +43,44 @@ void power_init(void)
 
     /* DOWN1CTL: CPU DVM step time = 30us (default: no DVM) */
     pmu_write(0x20, 2);
+
+    /* USB power configuration:
+     *
+     * GPIO C0 is probably related to the LTC4066's CLPROG
+     * pin (see datasheet). Setting it high allows to double
+     * the maximum current selected by HPWR:
+     *
+     *  GPIO B6     GPIO C0     USB current
+     *  HPWR        CLPROG ???  limit (mA)
+     *  -------     ----------  -----------
+     *  0           0           100
+     *  1           0           500
+     *  0           1           200
+     *  1           1           1000 ??? (max.seen ~750mA)
+     *
+     * USB current limit includes battery charge and device
+     * consumption. Battery charge has it's own limit at
+     * 330~340 mA (configured using RPROG).
+     *
+     * Setting either of GPIO C1 or GPIO C2 disables battery
+     * charge, power needed for device consumptiom is drained
+     * from USB or AC adaptor when present. If external power
+     * is not present or it is insufficient or limited,
+     * additional required power is drained from battery.
+     */
+    PCONB = (PCONB & 0x000000ff)
+          | (0xe << 8)      /* route D+ to ADC2: off */
+          | (0xe << 12)     /* route D- to ADC2: off */
+          | (0x0 << 16)     /* USB related input, POL pin ??? */
+          | (0x0 << 20)     /* USB related input, !CHRG pin ??? */
+          | (0xe << 24)     /* HPWR: 100mA */
+          | (0xe << 28);    /* USB suspend: off */
+
+    PCONC = (PCONC & 0xffff0000)
+          | (0xe << 0)      /* double HPWR limit: off */
+          | (0xe << 4)      /* disable battery charge: off */
+          | (0xe << 8)      /* disable battery charge: off */
+          | (0x0 << 12);    /* USB inserted/not inserted */
 }
 
 void ide_power_enable(bool on)