diff options
| author | Haavard Skinnemoen <haavard.skinnemoen@atmel.com> | 2008-04-30 00:52:17 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2008-04-30 08:29:31 -0700 |
| commit | 592e7bf80566bf5ac3ed073d4e198dd5b0824c04 (patch) | |
| tree | 8e778b8c93a16b11085099214f729b3795fd19a9 /drivers/spi | |
| parent | c6495aaabfaa8256c292c54b48ab081f4d86ad79 (diff) | |
atmel_spi: clean up baud rate divisor calculation
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>
Diffstat (limited to 'drivers/spi')
| -rw-r--r-- | drivers/spi/atmel_spi.c | 29 |
1 files changed, 20 insertions, 9 deletions
diff --git a/drivers/spi/atmel_spi.c b/drivers/spi/atmel_spi.c index 02c8e305b14..e81d59d7891 100644 --- a/drivers/spi/atmel_spi.c +++ b/drivers/spi/atmel_spi.c @@ -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); |