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spi_dw: use SPI bus frequency in spi_dw_configure()

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The SPI API states:

"max_sys_freq is the maximum frequency supported by the slave it
will deal with"

However, currently, for DW the max_sys_freq is a divider which confuses
the user.

This patch adds a small hack to allow users to use both dividers and
frequencies when configuring the bus. The only trade-off is one has to
use dividers for bus frequencies smaller than 65536Hz. However, since
most devices nowadays can run at clock frequencies more than 100kHz,
this is a good compromise.

Change-Id: I44386cc8ad501b08eeaf71bc7588661ff36e108b
Signed-off-by: Laurentiu Palcu <laurentiu.palcu@intel.com>
This commit is contained in:
Laurentiu Palcu 2016-04-01 09:41:30 +03:00 committed by Anas Nashif
parent dbe2c5faff
commit 7dd2372dd5
1 changed files with 18 additions and 2 deletions
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20
drivers/spi/spi_dw.c
View file

@ -58,6 +58,9 @@
#endif /* CONFIG_STDOUT_CONSOLE */
#endif /* CONFIG_SPI_DEBUG */
#define SPI_DW_CLK_DIVIDER(ssi_clk_hz) \
((CONFIG_SYS_CLOCK_HW_CYCLES_PER_SEC / ssi_clk_hz) & 0xFFFF)
static void completed(struct device *dev, int error)
{
struct spi_dw_config *info = dev->config->config_info;
@ -237,8 +240,21 @@ static int spi_dw_configure(struct device *dev,
/* Installing the configuration */
write_ctrlr0(ctrlr0, info->regs);
/* Configuring the rate */
write_baudr(config->max_sys_freq, info->regs);
/*
* Configure the rate. Use this small hack to allow the user to call
* spi_configure() with both a divider (as the driver was initially
* written) and a frequency (as the SPI API suggests to). The clock
* divider is a 16bit value, hence we can fairly, and safely, assume
* that everything above this value is a frequency. The trade-off is
* that if one wants to use a bus frequency of 64kHz (or less), it has
* the use a divider...
*/
if (config->max_sys_freq > 0xffff) {
write_baudr(SPI_DW_CLK_DIVIDER(config->max_sys_freq),
info->regs);
} else {
write_baudr(config->max_sys_freq, info->regs);
}
return 0;
}