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atmel_spi: clean up baud rate divisor calculation

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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.

[david-b@pacbell.net: fix it]
Signed-off-by: Haavard Skinnemoen <haavard.skinnemoen@atmel.com>
Cc: "Janesh Ramakrishnan" <jramakrishnan@neuropace.com>
Acked-by David Brownell <david-b@pacbell.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Haavard Skinnemoen 2008-04-30 00:52:17 -07:00 committed by Linus Torvalds
parent c6495aaabf
commit 592e7bf805
1 changed files with 20 additions and 9 deletions
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29
drivers/spi/atmel_spi.c
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@ -497,7 +497,7 @@ static int atmel_spi_setup(struct spi_device *spi)
struct atmel_spi *as;
u32 scbr, csr;
unsigned int bits = spi->bits_per_word;
unsigned long bus_hz, sck_hz;
unsigned long bus_hz;
unsigned int npcs_pin;
int ret;
@ -536,14 +536,25 @@ static int atmel_spi_setup(struct spi_device *spi)
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_device *spi)
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)
@ -589,7 +600,7 @@ static int atmel_spi_setup(struct spi_device *spi)
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);
bus_hz / scbr, bits, spi->mode, spi->chip_select, csr);
spi_writel(as, CSR0 + 4 * spi->chip_select, csr);