The patch titled
atmel_spi: Clean up baud rate divisor calculation
has been added to the -mm tree. Its filename is
atmel_spi-clean-up-baud-rate-divisor-calculation.patch
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Subject: atmel_spi: Clean up baud rate divisor calculation
From: Haavard Skinnemoen <haavard.skinnemoen@xxxxxxxxx>
Make the baud rate divisor calculation code a bit more readable and add a
few comments.
Also fix wrong debug information being displayed when !new_1 and
max_speed_hz == 0.
Signed-off-by: Haavard Skinnemoen <haavard.skinnemoen@xxxxxxxxx>
Cc: "Janesh Ramakrishnan" <jramakrishnan@xxxxxxxxxxxxx>
Cc: David Brownell <david-b@xxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
drivers/spi/atmel_spi.c | 26 +++++++++++++++++++-------
1 file changed, 19 insertions(+), 7 deletions(-)
diff -puN drivers/spi/atmel_spi.c~atmel_spi-clean-up-baud-rate-divisor-calculation drivers/spi/atmel_spi.c
--- a/drivers/spi/atmel_spi.c~atmel_spi-clean-up-baud-rate-divisor-calculation
+++ a/drivers/spi/atmel_spi.c
@@ -536,14 +536,25 @@ static int atmel_spi_setup(struct spi_de
return -EINVAL;
}
- /* speed zero convention is used by some upper layers */
+ /*
+ * Pre-new_1 chips start out at half the peripheral
+ * bus speed.
+ */
bus_hz = clk_get_rate(as->clk);
+ if (!as->new_1)
+ bus_hz /= 2;
+
if (spi->max_speed_hz) {
- /* assume div32/fdiv/mbz == 0 */
- if (!as->new_1)
- bus_hz /= 2;
- scbr = ((bus_hz + spi->max_speed_hz - 1)
- / spi->max_speed_hz);
+ /*
+ * Calculate the lowest divider that satisfies the
+ * constraint, assuming div32/fdiv/mbz == 0.
+ */
+ scbr = DIV_ROUND_UP(bus_hz, spi->max_speed_hz);
+
+ /*
+ * If the resulting divider doesn't fit into the
+ * register bitfield, we can't satisfy the constraint.
+ */
if (scbr >= (1 << SPI_SCBR_SIZE)) {
dev_dbg(&spi->dev,
"setup: %d Hz too slow, scbr %u; min %ld Hz\n",
@@ -551,8 +562,8 @@ static int atmel_spi_setup(struct spi_de
return -EINVAL;
}
} else
+ /* speed zero means "as slow as possible" */
scbr = 0xff;
- sck_hz = bus_hz / scbr;
csr = SPI_BF(SCBR, scbr) | SPI_BF(BITS, bits - 8);
if (spi->mode & SPI_CPOL)
@@ -587,6 +598,7 @@ static int atmel_spi_setup(struct spi_de
spin_unlock_irqrestore(&as->lock, flags);
}
+ sck_hz = bus_hz / scbr;
dev_dbg(&spi->dev,
"setup: %lu Hz bpw %u mode 0x%x -> csr%d %08x\n",
sck_hz, bits, spi->mode, spi->chip_select, csr);
_
Patches currently in -mm which might be from haavard.skinnemoen@xxxxxxxxx are
origin.patch
atmel_spi-clean-up-baud-rate-divisor-calculation.patch
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