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spi/davinci: Fix clock prescale factor computation

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Computation of the clock prescaler value returned bogus results if
the requested SPI clock was impossible to set. It now sets either
the maximum or minimum clock frequency, as appropriate.

Signed-off-by: Thomas Koeller <thomas.koeller@baslerweb.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
This commit is contained in:
Thomas Koeller 2010-04-26 09:01:45 +00:00 committed by Grant Likely
parent 41c4221ca6
commit 0c2a2ae327
1 changed files with 9 additions and 3 deletions
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12
drivers/spi/davinci_spi.c
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@ -301,7 +301,7 @@ static int davinci_spi_setup_transfer(struct spi_device *spi,
struct davinci_spi *davinci_spi;
struct davinci_spi_platform_data *pdata;
u8 bits_per_word = 0;
u32 hz = 0, prescale;
u32 hz = 0, prescale = 0, clkspeed;
davinci_spi = spi_master_get_devdata(spi->master);
pdata = davinci_spi->pdata;
@ -338,10 +338,16 @@ static int davinci_spi_setup_transfer(struct spi_device *spi,
set_fmt_bits(davinci_spi->base, bits_per_word & 0x1f,
spi->chip_select);
prescale = ((clk_get_rate(davinci_spi->clk) / hz) - 1) & 0xff;
clkspeed = clk_get_rate(davinci_spi->clk);
if (hz > clkspeed / 2)
prescale = 1 << 8;
if (hz < clkspeed / 256)
prescale = 255 << 8;
if (!prescale)
prescale = ((clkspeed / hz - 1) << 8) & 0x0000ff00;
clear_fmt_bits(davinci_spi->base, 0x0000ff00, spi->chip_select);
set_fmt_bits(davinci_spi->base, prescale << 8, spi->chip_select);
set_fmt_bits(davinci_spi->base, prescale, spi->chip_select);
return 0;
}