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Date: Wed, 26 Nov 2008 22:54:17 +0300
From: Anton Vorontsov <avorontsov@...mvista.com>
To: Pierre Ossman <drzeus-mmc@...eus.cx>
Cc: linux-kernel@...r.kernel.org, linuxppc-dev@...abs.org,
David Brownell <dbrownell@...rs.sourceforge.net>,
Grant Likely <grant.likely@...retlab.ca>
Subject: [PATCH v2] 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@...mvista.com>
---
Hi Pierre,
Sorry for the delay.
On Sat, Nov 08, 2008 at 09:55:37PM +0100, Pierre Ossman wrote:
> On Thu, 30 Oct 2008 22:56:32 +0300
> Anton Vorontsov <avorontsov@...mvista.com> 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.
Yeah, makes sense. Now the function returns OCR mask, or 0 on error.
> > + /* 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).
Something like this patch (the boundary cases are documented now)?
p.s. If the patch is OK I'll respin the whole patchset.
drivers/mmc/core/core.c | 75 ++++++++++++++++++++++++++++++++++++++++++++++
include/linux/mmc/core.h | 2 +
2 files changed, 77 insertions(+), 0 deletions(-)
diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
index 044d84e..1673765 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 +445,80 @@ 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
diff --git a/include/linux/mmc/core.h b/include/linux/mmc/core.h
index 143cebf..7ac8b50 100644
--- a/include/linux/mmc/core.h
+++ b/include/linux/mmc/core.h
@@ -151,4 +151,6 @@ static inline void mmc_claim_host(struct mmc_host *host)
__mmc_claim_host(host, NULL);
}
+extern u32 mmc_vddrange_to_ocrmask(int vdd_min, int vdd_max);
+
#endif
--
1.5.6.5
--
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