Calculate the divisor for the SCR (Serial Clock Rate), avoidingReviewed-by: Jarkko Nikula <jarkko.nikula@xxxxxxxxxxxxxxx>
that the SSP transmission rate can be greater than the device rate.
When the division between the SSP clock and the device rate generates
a reminder, we have to increment by one the divisor.
In this way the resulting SSP clock will never be greater than the
device SPI max frequency.
For example, with:
- ssp_clk = 50 MHz
- dev freq = 15 MHz
without this patch the SSP clock will be greater than 15 MHz:
- 25 MHz for PXA25x_SSP and CE4100_SSP
- 16,56 MHz for the others
Instead, with this patch, we have in both case an SSP clock of 12.5MHz,
so the max rate of the SPI device clock is respected.
Signed-off-by: Flavio Suligoi <f.suligoi@xxxxxxx>
Reviewed-by: Jarkko Nikula <jarkko.nikula@xxxxxxxxxxxxxxx>
---
v2: - simplify the code using "DIV_ROUND_UP"
v1: - first version
drivers/spi/spi-pxa2xx.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/drivers/spi/spi-pxa2xx.c b/drivers/spi/spi-pxa2xx.c
index f7068cc..a35fdcb 100644
--- a/drivers/spi/spi-pxa2xx.c
+++ b/drivers/spi/spi-pxa2xx.c
@@ -884,10 +884,14 @@ static unsigned int ssp_get_clk_div(struct driver_data *drv_data, int rate)
rate = min_t(int, ssp_clk, rate);
+ /*
+ * Calculate the divisor for the SCR (Serial Clock Rate), avoiding
+ * that the SSP transmission rate can be greater than the device rate
+ */
if (ssp->type == PXA25x_SSP || ssp->type == CE4100_SSP)
- return (ssp_clk / (2 * rate) - 1) & 0xff;
+ return (DIV_ROUND_UP(ssp_clk, 2 * rate) - 1) & 0xff;
else
- return (ssp_clk / rate - 1) & 0xfff;
+ return (DIV_ROUND_UP(ssp_clk, rate) - 1) & 0xfff;
}