mmc: Add mmc_vddrange_to_ocrmask() helper function

This function sets the OCR mask bits according to provided voltage
ranges. Will be used by the mmc_spi OpenFirmware bindings.

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>

1 files changed, 75 insertions, 0 deletions

diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
index f7284b905eb3..5f288aeeb721 100644
--- a/drivers/mmc/core/core.c
+++ b/drivers/mmc/core/core.c
@@ -20,6 +20,7 @@
 #include <linux/err.h>
 #include <linux/leds.h>
 #include <linux/scatterlist.h>
+#include <linux/log2.h>
 
 #include <linux/mmc/card.h>
 #include <linux/mmc/host.h>
@@ -448,6 +449,80 @@ void mmc_set_bus_width(struct mmc_host *host, unsigned int width)
         mmc_set_ios(host);
 }
 
+/**
+ * mmc_vdd_to_ocrbitnum - Convert a voltage to the OCR bit number
+ * @vdd:        voltage (mV)
+ * @low_bits:   prefer low bits in boundary cases
+ *
+ * This function returns the OCR bit number according to the provided @vdd
+ * value. If conversion is not possible a negative errno value returned.
+ *
+ * Depending on the @low_bits flag the function prefers low or high OCR bits
+ * on boundary voltages. For example,
+ * with @low_bits = true, 3300 mV translates to ilog2(MMC_VDD_32_33);
+ * with @low_bits = false, 3300 mV translates to ilog2(MMC_VDD_33_34);
+ *
+ * Any value in the [1951:1999] range translates to the ilog2(MMC_VDD_20_21).
+ */
+static int mmc_vdd_to_ocrbitnum(int vdd, bool low_bits)
+{
+        const int max_bit = ilog2(MMC_VDD_35_36);
+        int bit;
+
+        if (vdd < 1650 || vdd > 3600)
+                return -EINVAL;
+
+        if (vdd >= 1650 && vdd <= 1950)
+                return ilog2(MMC_VDD_165_195);
+
+        if (low_bits)
+                vdd -= 1;
+
+        /* Base 2000 mV, step 100 mV, bit's base 8. */
+        bit = (vdd - 2000) / 100 + 8;
+        if (bit > max_bit)
+                return max_bit;
+        return bit;
+}
+
+/**
+ * mmc_vddrange_to_ocrmask - Convert a voltage range to the OCR mask
+ * @vdd_min:    minimum voltage value (mV)
+ * @vdd_max:    maximum voltage value (mV)
+ *
+ * This function returns the OCR mask bits according to the provided @vdd_min
+ * and @vdd_max values. If conversion is not possible the function returns 0.
+ *
+ * Notes wrt boundary cases:
+ * This function sets the OCR bits for all boundary voltages, for example
+ * [3300:3400] range is translated to MMC_VDD_32_33 | MMC_VDD_33_34 |
+ * MMC_VDD_34_35 mask.
+ */
+u32 mmc_vddrange_to_ocrmask(int vdd_min, int vdd_max)
+{
+        u32 mask = 0;
+
+        if (vdd_max < vdd_min)
+                return 0;
+
+        /* Prefer high bits for the boundary vdd_max values. */
+        vdd_max = mmc_vdd_to_ocrbitnum(vdd_max, false);
+        if (vdd_max < 0)
+                return 0;
+
+        /* Prefer low bits for the boundary vdd_min values. */
+        vdd_min = mmc_vdd_to_ocrbitnum(vdd_min, true);
+        if (vdd_min < 0)
+                return 0;
+
+        /* Fill the mask, from max bit to min bit. */
+        while (vdd_max >= vdd_min)
+                mask |= 1 << vdd_max--;
+
+        return mask;
+}
+EXPORT_SYMBOL(mmc_vddrange_to_ocrmask);
+
 /*
  * Mask off any voltages we don't support and select
  * the lowest voltage