mmc: core: eMMC 4.5 Power Class Selection Feature

This patch adds the power class selection feature available for mmc
versions 4.0 and above.  During the enumeration stage before switching
to the lower data bus, check if the power class is supported for the
current bus width. If the power class is available then switch to the
power class and use the higher data bus. If power class is not supported
then switch to the lower data bus in a worst case.
Signed-off-by: Girish K S <girish.shivananjappa@linaro.org>
Signed-off-by: Chris Ball <cjb@laptop.org>

drivers/mmc/core/mmc.c

@@ -531,6 +531,86 @@ static struct device_type mmc_type = {
 	.groups = mmc_attr_groups,
 };
 
+/*
+ * Select the PowerClass for the current bus width
+ * If power class is defined for 4/8 bit bus in the
+ * extended CSD register, select it by executing the
+ * mmc_switch command.
+ */
+static int mmc_select_powerclass(struct mmc_card *card,
+		unsigned int bus_width, u8 *ext_csd)
+{
+	int err = 0;
+	unsigned int pwrclass_val;
+	unsigned int index = 0;
+	struct mmc_host *host;
+
+	BUG_ON(!card);
+
+	host = card->host;
+	BUG_ON(!host);
+
+	if (ext_csd == NULL)
+		return 0;
+
+	/* Power class selection is supported for versions >= 4.0 */
+	if (card->csd.mmca_vsn < CSD_SPEC_VER_4)
+		return 0;
+
+	/* Power class values are defined only for 4/8 bit bus */
+	if (bus_width == EXT_CSD_BUS_WIDTH_1)
+		return 0;
+
+	switch (1 << host->ios.vdd) {
+	case MMC_VDD_165_195:
+		if (host->ios.clock <= 26000000)
+			index = EXT_CSD_PWR_CL_26_195;
+		else if	(host->ios.clock <= 52000000)
+			index = (bus_width <= EXT_CSD_BUS_WIDTH_8) ?
+				EXT_CSD_PWR_CL_52_195 :
+				EXT_CSD_PWR_CL_DDR_52_195;
+		else if (host->ios.clock <= 200000000)
+			index = EXT_CSD_PWR_CL_200_195;
+		break;
+	case MMC_VDD_32_33:
+	case MMC_VDD_33_34:
+	case MMC_VDD_34_35:
+	case MMC_VDD_35_36:
+		if (host->ios.clock <= 26000000)
+			index = EXT_CSD_PWR_CL_26_360;
+		else if	(host->ios.clock <= 52000000)
+			index = (bus_width <= EXT_CSD_BUS_WIDTH_8) ?
+				EXT_CSD_PWR_CL_52_360 :
+				EXT_CSD_PWR_CL_DDR_52_360;
+		else if (host->ios.clock <= 200000000)
+			index = EXT_CSD_PWR_CL_200_360;
+		break;
+	default:
+		pr_warning("%s: Voltage range not supported "
+			   "for power class.\n", mmc_hostname(host));
+		return -EINVAL;
+	}
+
+	pwrclass_val = ext_csd[index];
+
+	if (bus_width & (EXT_CSD_BUS_WIDTH_8 | EXT_CSD_DDR_BUS_WIDTH_8))
+		pwrclass_val = (pwrclass_val & EXT_CSD_PWR_CL_8BIT_MASK) >>
+				EXT_CSD_PWR_CL_8BIT_SHIFT;
+	else
+		pwrclass_val = (pwrclass_val & EXT_CSD_PWR_CL_4BIT_MASK) >>
+				EXT_CSD_PWR_CL_4BIT_SHIFT;
+
+	/* If the power class is different from the default value */
+	if (pwrclass_val > 0) {
+		err = mmc_switch(card, EXT_CSD_CMD_SET_NORMAL,
+				 EXT_CSD_POWER_CLASS,
+				 pwrclass_val,
+				 0);
+	}
+
+	return err;
+}
+
 /*
  * Handle the detection and initialisation of a card.
  *
@@ -787,6 +867,14 @@ static int mmc_init_card(struct mmc_host *host, u32 ocr,
 			bus_width = bus_widths[idx];
 			if (bus_width == MMC_BUS_WIDTH_1)
 				ddr = 0; /* no DDR for 1-bit width */
+			err = mmc_select_powerclass(card, ext_csd_bits[idx][0],
+						    ext_csd);
+			if (err)
+				pr_err("%s: power class selection to "
+				       "bus width %d failed\n",
+				       mmc_hostname(card->host),
+				       1 << bus_width);
+
 			err = mmc_switch(card, EXT_CSD_CMD_SET_NORMAL,
 					 EXT_CSD_BUS_WIDTH,
 					 ext_csd_bits[idx][0],
@@ -810,6 +898,14 @@ static int mmc_init_card(struct mmc_host *host, u32 ocr,
 		}
 
 		if (!err && ddr) {
+			err = mmc_select_powerclass(card, ext_csd_bits[idx][1],
+						    ext_csd);
+			if (err)
+				pr_err("%s: power class selection to "
+				       "bus width %d ddr %d failed\n",
+				       mmc_hostname(card->host),
+				       1 << bus_width, ddr);
+
 			err = mmc_switch(card, EXT_CSD_CMD_SET_NORMAL,
 					 EXT_CSD_BUS_WIDTH,
 					 ext_csd_bits[idx][1],

include/linux/mmc/mmc.h

@@ -279,10 +279,15 @@ struct _mmc_csd {
 #define EXT_CSD_ERASED_MEM_CONT		181	/* RO */
 #define EXT_CSD_BUS_WIDTH		183	/* R/W */
 #define EXT_CSD_HS_TIMING		185	/* R/W */
+#define EXT_CSD_POWER_CLASS		187	/* R/W */
 #define EXT_CSD_REV			192	/* RO */
 #define EXT_CSD_STRUCTURE		194	/* RO */
 #define EXT_CSD_CARD_TYPE		196	/* RO */
 #define EXT_CSD_PART_SWITCH_TIME        199     /* RO */
+#define EXT_CSD_PWR_CL_52_195		200	/* RO */
+#define EXT_CSD_PWR_CL_26_195		201	/* RO */
+#define EXT_CSD_PWR_CL_52_360		202	/* RO */
+#define EXT_CSD_PWR_CL_26_360		203	/* RO */
 #define EXT_CSD_SEC_CNT			212	/* RO, 4 bytes */
 #define EXT_CSD_S_A_TIMEOUT		217	/* RO */
 #define EXT_CSD_REL_WR_SEC_C		222	/* RO */
@@ -294,6 +299,11 @@ struct _mmc_csd {
 #define EXT_CSD_SEC_ERASE_MULT		230	/* RO */
 #define EXT_CSD_SEC_FEATURE_SUPPORT	231	/* RO */
 #define EXT_CSD_TRIM_MULT		232	/* RO */
+#define EXT_CSD_PWR_CL_200_195		236	/* RO */
+#define EXT_CSD_PWR_CL_200_360		237	/* RO */
+#define EXT_CSD_PWR_CL_DDR_52_195	238	/* RO */
+#define EXT_CSD_PWR_CL_DDR_52_360	239	/* RO */
+#define EXT_CSD_POWER_OFF_LONG_TIME	247	/* RO */
 
 /*
  * EXT_CSD field definitions
@@ -332,6 +342,10 @@ struct _mmc_csd {
 #define EXT_CSD_RST_N_EN_MASK	0x3
 #define EXT_CSD_RST_N_ENABLED	1	/* RST_n is enabled on card */
 
+#define EXT_CSD_PWR_CL_8BIT_MASK	0xF0	/* 8 bit PWR CLS */
+#define EXT_CSD_PWR_CL_4BIT_MASK	0x0F	/* 8 bit PWR CLS */
+#define EXT_CSD_PWR_CL_8BIT_SHIFT	4
+#define EXT_CSD_PWR_CL_4BIT_SHIFT	0
 /*
  * MMC_SWITCH access modes
  */