Re: [PATCH 2/3] mmc: Add mmc_vddrange_to_ocrmask() helper function

[Pierre Ossman]

On Thu, 30 Oct 2008 22:56:32 +0300
Anton Vorontsov [EMAIL PROTECTED] wrote:

 +/**
 + * mmc_vddrange_to_ocrmask - Convert a voltage range to the OCR mask
 + * @vdd_min: minimum voltage value (mV)
 + * @vdd_max: maximum voltage value (mV)
 + * @mask:pointer to the mask
 + *

Why the pointer? Why not let the caller handle the aggregation? That
would be a lot safer.

 + /* fill the mask, from max bit to min bit */
 + while (vdd_max = vdd_min)
 + *mask |= 1  vdd_max--;
 + return 0;

Many cards get a bit uppity with a single bit set. If possible, try to
make this function set two bits when the voltage is right on the
boundary (e.g. 3.3V).

Rgds
-- 
 -- Pierre Ossman

  Linux kernel, MMC maintainerhttp://www.kernel.org
  rdesktop, core developer  http://www.rdesktop.org

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[PATCH 2/3] mmc: Add mmc_vddrange_to_ocrmask() helper function

[Anton Vorontsov]

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 [EMAIL PROTECTED]
---
 drivers/mmc/core/core.c  |   55 ++
 include/linux/mmc/core.h |3 ++
 2 files changed, 58 insertions(+), 0 deletions(-)

diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
index 044d84e..d4afae8 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
@@ -444,6 +445,60 @@ void mmc_set_bus_width(struct mmc_host *host, unsigned int 
width)
mmc_set_ios(host);
 }
 
+static int mmc_vdd_to_ocrbit(int vdd)
+{
+   int bit;
+   const int max_bit = ilog2(MMC_VDD_35_36);
+
+   if (vdd  1650 || vdd  3600)
+   return -EINVAL;
+
+   if (vdd = 1650  vdd = 1950)
+   return ilog2(MMC_VDD_165_195);
+
+   /* 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)
+ * @mask:  pointer to the mask
+ *
+ * This function sets the OCR mask bits according to the provided @vdd_min
+ * and @vdd_max values.
+ *
+ * NOTE: You _must_ set the mask value to 0 before calling this function the
+ *   first time. This is done so that you can call this function several
+ *   times to set OCR mask for discontinuous voltage ranges.
+ *
+ * The function returns 0 on success and a negative errno value when
+ * a conversion is not possible.
+ */
+int mmc_vddrange_to_ocrmask(int vdd_min, int vdd_max, unsigned int *mask)
+{
+   if (vdd_max  vdd_min)
+   return -EINVAL;
+
+   vdd_max = mmc_vdd_to_ocrbit(vdd_max);
+   if (vdd_max  0)
+   return -EINVAL;
+
+   vdd_min = mmc_vdd_to_ocrbit(vdd_min);
+   if (vdd_min  0)
+   return -EINVAL;
+
+   /* fill the mask, from max bit to min bit */
+   while (vdd_max = vdd_min)
+   *mask |= 1  vdd_max--;
+   return 0;
+}
+EXPORT_SYMBOL(mmc_vddrange_to_ocrmask);
+
 /*
  * Mask off any voltages we don't support and select
  * the lowest voltage
diff --git a/include/linux/mmc/core.h b/include/linux/mmc/core.h
index 143cebf..3b139b0 100644
--- a/include/linux/mmc/core.h
+++ b/include/linux/mmc/core.h
@@ -151,4 +151,7 @@ static inline void mmc_claim_host(struct mmc_host *host)
__mmc_claim_host(host, NULL);
 }
 
+extern int mmc_vddrange_to_ocrmask(int vdd_min, int vdd_max,
+  unsigned int *mask);
+
 #endif
-- 
1.5.6.3

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