diff options
Diffstat (limited to 'drivers/spi')
| -rw-r--r-- | drivers/spi/davinci_spi.c | 53 |
1 files changed, 31 insertions, 22 deletions
diff --git a/drivers/spi/davinci_spi.c b/drivers/spi/davinci_spi.c index d5d7014e6ae2..17269ad54a99 100644 --- a/drivers/spi/davinci_spi.c +++ b/drivers/spi/davinci_spi.c @@ -53,6 +53,7 @@ #define SPIFMT_WDELAY_MASK 0x3f000000u #define SPIFMT_WDELAY_SHIFT 24 #define SPIFMT_CHARLEN_MASK 0x0000001Fu +#define SPIFMT_PRESCALE_SHIFT 8 /* SPIPC0 */ @@ -267,6 +268,29 @@ static void davinci_spi_chipselect(struct spi_device *spi, int value) } /** + * davinci_spi_get_prescale - Calculates the correct prescale value + * @maxspeed_hz: the maximum rate the SPI clock can run at + * + * This function calculates the prescale value that generates a clock rate + * less than or equal to the specified maximum. + * + * Returns: calculated prescale - 1 for easy programming into SPI registers + * or negative error number if valid prescalar cannot be updated. + */ +static inline int davinci_spi_get_prescale(struct davinci_spi *davinci_spi, + u32 max_speed_hz) +{ + int ret; + + ret = DIV_ROUND_UP(clk_get_rate(davinci_spi->clk), max_speed_hz); + + if (ret < 3 || ret > 256) + return -EINVAL; + + return ret - 1; +} + +/** * davinci_spi_setup_transfer - This functions will determine transfer method * @spi: spi device on which data transfer to be done * @t: spi transfer in which transfer info is filled @@ -281,7 +305,7 @@ static int davinci_spi_setup_transfer(struct spi_device *spi, struct davinci_spi *davinci_spi; u8 bits_per_word = 0; - u32 hz = 0, prescale = 0, clkspeed; + u32 hz = 0, prescale = 0; davinci_spi = spi_master_get_devdata(spi->master); @@ -312,21 +336,18 @@ static int davinci_spi_setup_transfer(struct spi_device *spi, if (!hz) hz = spi->max_speed_hz; + prescale = davinci_spi_get_prescale(davinci_spi, hz); + if (prescale < 0) + return prescale; + clear_fmt_bits(davinci_spi->base, SPIFMT_CHARLEN_MASK, spi->chip_select); set_fmt_bits(davinci_spi->base, bits_per_word & 0x1f, spi->chip_select); - 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, spi->chip_select); + set_fmt_bits(davinci_spi->base, + prescale << SPIFMT_PRESCALE_SHIFT, spi->chip_select); return 0; } @@ -413,10 +434,8 @@ static int davinci_spi_setup(struct spi_device *spi) int retval; struct davinci_spi *davinci_spi; struct davinci_spi_dma *davinci_spi_dma; - struct device *sdev; davinci_spi = spi_master_get_devdata(spi->master); - sdev = davinci_spi->bitbang.master->dev.parent; /* if bits per word length is zero then set it default 8 */ if (!spi->bits_per_word) @@ -436,16 +455,6 @@ static int davinci_spi_setup(struct spi_device *spi) } /* - * SPI in DaVinci and DA8xx operate between - * 600 KHz and 50 MHz - */ - if (spi->max_speed_hz < 600000 || spi->max_speed_hz > 50000000) { - dev_dbg(sdev, "Operating frequency is not in acceptable " - "range\n"); - return -EINVAL; - } - - /* * Set up SPIFMTn register, unique to this chipselect. * * NOTE: we could do all of these with one write. Also, some |