powerpc/t4240qds: Add VDD override

Allow VDD voltage overriding with a command. This is an add-on feasture of
VID. To override VDD, use command vdd_override with the value of voltage
in mV, for example

vdd_override <voltage in mV, eg. 1050>

The above example will set the VDD to 1.050 volt. Any wrong value out of
range of 0.8188 to 1.2125 volt or invalid string is ignored.

In addition to the command, if overriding VDD is needed earlier in booting
process, save an variable and reboot:

setenv t4240qds_vdd_mv <voltage in mV>
saveenv

Signed-off-by: York Sun <yorksun@freescale.com>
Signed-off-by: Andy Fleming <afleming@freescale.com>

board/freescale/t4qds/t4qds.c

@@ -234,7 +234,7 @@ static inline int set_voltage(u8 vid)
 }
 
 
-static int adjust_vdd(void)
+static int adjust_vdd(ulong vdd_override)
 {
 	int re_enable = disable_interrupts();
 	ccsr_gur_t __iomem *gur =
@@ -243,6 +243,8 @@ static int adjust_vdd(void)
 	u8 vid, vid_current;
 	int vdd_target, vdd_current, vdd_last;
 	int ret;
+	unsigned long vdd_string_override;
+	char *vdd_string;
 	static const uint16_t vdd[32] = {
 		0,	/* unused */
 		9875,	/* 0.9875V */
@@ -292,6 +294,19 @@ static int adjust_vdd(void)
 			FSL_CORENET_DCFG_FUSESR_ALTVID_MASK;
 	}
 	vdd_target = vdd[vid];
+
+	/* check override variable for overriding VDD */
+	vdd_string = getenv("t4240qds_vdd_mv");
+	if (vdd_override == 0 && vdd_string &&
+	    !strict_strtoul(vdd_string, 10, &vdd_string_override))
+		vdd_override = vdd_string_override;
+	if (vdd_override >= 819 && vdd_override <= 1212) {
+		vdd_target = vdd_override * 10; /* convert to 1/10 mV */
+		debug("VDD override is %lu\n", vdd_override);
+	} else if (vdd_override != 0) {
+		printf("Invalid value.\n");
+	}
+
 	if (vdd_target == 0) {
 		debug("VID: VID not used\n");
 		ret = 0;
@@ -511,7 +526,7 @@ int board_early_init_r(void)
 	 * Adjust core voltage according to voltage ID
 	 * This function changes I2C mux to channel 2.
 	 */
-	if (adjust_vdd())
+	if (adjust_vdd(0))
 		printf("Warning: Adjusting core voltage failed.\n");
 
 	/* Configure board SERDES ports crossbar */
@@ -801,3 +816,23 @@ void qixis_dump_switch(void)
 			i + 1, byte_to_binary_mask(sw[i], mask[i], buf), sw[i]);
 	}
 }
+
+static int do_vdd_adjust(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
+{
+	ulong override;
+
+	if (argc < 2)
+		return CMD_RET_USAGE;
+	if (!strict_strtoul(argv[1], 10, &override))
+		adjust_vdd(override);	/* the value is checked by callee */
+	else
+		return CMD_RET_USAGE;
+
+	return 0;
+}
+
+U_BOOT_CMD(
+	vdd_override, 2, 0, do_vdd_adjust,
+	"Override VDD",
+	"- override with the voltage specified in mV, eg. 1050"
+);

doc/README.t4240qds

@@ -96,3 +96,27 @@ The addresses in brackets are physical addresses.
 0x0_ffff_f000 (0x0_7fff_fff0) - 0x0_ffff_ffff   4KB Boot page translation for secondary cores
 
 The physical address of the last (boot page translation) varies with the actual DDR size.
+
+Voltage ID and VDD override
+--------------------
+T4240 has a VID feature. U-boot reads the VID efuses and adjust the voltage
+accordingly. The voltage can also be override by command vdd_override. The
+syntax is
+
+vdd_override <voltage in mV>, eg. 1050 is for 1.050v.
+
+Upon success, the actual voltage will be read back. The value is checked
+for safety and any invalid value will not adjust the voltage.
+
+Another way to override VDD is to use environmental variable, in case of using
+command is too late for some debugging. The syntax is
+
+setenv t4240qds_vdd_mv <voltage in mV>
+saveenv
+reset
+
+The override voltage takes effect when booting.
+
+Note: voltage adjustment needs to be done step by step. Changing voltage too
+rapidly may cause current surge. The voltage stepping is done by software.
+Users can set the final voltage directly.