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| author | Ben Dooks <ben@simtec.co.uk> | 2009-08-18 14:11:16 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2009-08-18 16:31:13 -0700 |
| commit | b8978784544e8b4e8fbacb558df8580957d4f8a5 (patch) | |
| tree | ecc74e896383a4203d0bdd679161bd419f4b430e /drivers/spi | |
| parent | b2503a9408e44eb0531adc3436c513ea70f91c42 (diff) | |
| download | linux-b8978784544e8b4e8fbacb558df8580957d4f8a5.tar.gz linux-b8978784544e8b4e8fbacb558df8580957d4f8a5.tar.bz2 linux-b8978784544e8b4e8fbacb558df8580957d4f8a5.zip | |
spi_s3c24xx: fix clock rate calculation
Currently the clock rate calculation may round as pleased, which means
that it is possible that we will round down and end up with a faster clock
rate than intended.
Change the calculation to use DIV_ROUND_UP() to ensure that we end up with
a clock rate either the same as or lower than the user requested one.
Signed-off-by: Ben Dooks <ben@simtec.co.uk>
Cc: 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/spi_s3c24xx.c | 17 |
1 files changed, 7 insertions, 10 deletions
diff --git a/drivers/spi/spi_s3c24xx.c b/drivers/spi/spi_s3c24xx.c index e0d44af4745a..590be85c8f3d 100644 --- a/drivers/spi/spi_s3c24xx.c +++ b/drivers/spi/spi_s3c24xx.c @@ -111,6 +111,7 @@ static int s3c24xx_spi_setupxfer(struct spi_device *spi, unsigned int bpw; unsigned int hz; unsigned int div; + unsigned long clk; bpw = t ? t->bits_per_word : spi->bits_per_word; hz = t ? t->speed_hz : spi->max_speed_hz; @@ -120,20 +121,16 @@ static int s3c24xx_spi_setupxfer(struct spi_device *spi, return -EINVAL; } - div = clk_get_rate(hw->clk) / hz; - - /* is clk = pclk / (2 * (pre+1)), or is it - * clk = (pclk * 2) / ( pre + 1) */ - - div /= 2; - - if (div > 0) - div -= 1; + clk = clk_get_rate(hw->clk); + div = DIV_ROUND_UP(clk, hz * 2) - 1; if (div > 255) div = 255; - dev_dbg(&spi->dev, "setting pre-scaler to %d (hz %d)\n", div, hz); + dev_dbg(&spi->dev, "setting pre-scaler to %d (wanted %d, got %ld)\n", + div, hz, clk / (2 * (div + 1))); + + writeb(div, hw->regs + S3C2410_SPPRE); spin_lock(&hw->bitbang.lock); |