From: Ben Dooks <ben@simtec.co.uk>
To: spi-devel-general@lists.sourceforge.net, dbrownell@users.sourceforge.ne
Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org
Subject: [patch 2/7] spi_s3c24xx: fix clock rate calculation
Date: Thu, 13 Aug 2009 11:06:04 +0100 [thread overview]
Message-ID: <20090813100638.423180765@fluff.org> (raw)
In-Reply-To: 20090813100602.545180197@fluff.org
[-- Attachment #1: spi-fix-buad-generation.patch --]
[-- Type: text/plain, Size: 1565 bytes --]
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>
---
drivers/spi/spi_s3c24xx.c | 17 +++++++----------
1 file changed, 7 insertions(+), 10 deletions(-)
Index: b/drivers/spi/spi_s3c24xx.c
===================================================================
--- a/drivers/spi/spi_s3c24xx.c 2009-07-14 13:56:07.000000000 +0100
+++ b/drivers/spi/spi_s3c24xx.c 2009-07-14 14:08:45.000000000 +0100
@@ -111,6 +111,7 @@ static int s3c24xx_spi_setupxfer(struct
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
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);
--
next prev parent reply other threads:[~2009-08-13 10:06 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-08-13 10:06 [patch 0/7] SPI fixes for documentation and spi_s3c24xx driver Ben Dooks
2009-08-13 10:06 ` [patch 1/7] spi: fix spelling of automatically in documentation Ben Dooks
2009-08-13 10:06 ` Ben Dooks [this message]
2009-08-13 10:06 ` [patch 3/7] spi_s3c24xx; Fix transfer setup code Ben Dooks
2009-08-13 10:06 ` [patch 4/7] spi_s3c24xx: fix header includes Ben Dooks
2009-08-13 10:06 ` [patch 5/7] spi_s3c24xx: use resource_size() to get resource size Ben Dooks
2009-08-13 10:06 ` [patch 6/7] spi_s3c24xx: use dev_pm_ops Ben Dooks
2009-08-13 10:06 ` [patch 7/7] spi_s3c24xx: cache device setup data Ben Dooks
2009-08-13 21:24 ` [patch 0/7] SPI fixes for documentation and spi_s3c24xx driver Andrew Morton
2009-08-14 14:06 ` Ben Dooks
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