From: Marc Kleine-Budde <mkl@xxxxxxxxxxxxxx>
[ Upstream commit ed7815db70d17b1741883f2da8e1d80bc2efe517 ]
A SPI transfer defines the _maximum_ speed of the SPI transfer. However the
driver doesn't take into account that the clock divider is always rounded down
(due to integer arithmetics). This results in a too high clock rate for the SPI
transfer.
E.g.: with a mclk_rate of 24 MHz and a SPI transfer speed of 10 MHz, the
original code calculates a reg of "0", which results in a effective divider of
"2" and a 12 MHz clock for the SPI transfer.
This patch fixes the issue by using DIV_ROUND_UP() instead of a plain
integer division.
While there simplify the divider calculation for the CDR1 case, use
order_base_2() instead of two ilog2() calculations.
Fixes: 3558fe900e8a ("spi: sunxi: Add Allwinner A31 SPI controller driver")
Signed-off-by: Marc Kleine-Budde <mkl@xxxxxxxxxxxxxx>
Acked-by: Maxime Ripard <mripard@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20200706143443.9855-2-mkl@xxxxxxxxxxxxxx
Signed-off-by: Mark Brown <broonie@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
drivers/spi/spi-sun6i.c | 14 ++++++--------
1 file changed, 6 insertions(+), 8 deletions(-)
diff --git a/drivers/spi/spi-sun6i.c b/drivers/spi/spi-sun6i.c
index 8533f4edd00af..21a22d42818c8 100644
--- a/drivers/spi/spi-sun6i.c
+++ b/drivers/spi/spi-sun6i.c
@@ -202,7 +202,7 @@ static int sun6i_spi_transfer_one(struct spi_master *master,
struct spi_transfer *tfr)
{
struct sun6i_spi *sspi = spi_master_get_devdata(master);
- unsigned int mclk_rate, div, timeout;
+ unsigned int mclk_rate, div, div_cdr1, div_cdr2, timeout;
unsigned int start, end, tx_time;
unsigned int trig_level;
unsigned int tx_len = 0;
@@ -291,14 +291,12 @@ static int sun6i_spi_transfer_one(struct spi_master *master,
* First try CDR2, and if we can't reach the expected
* frequency, fall back to CDR1.
*/
- div = mclk_rate / (2 * tfr->speed_hz);
- if (div <= (SUN6I_CLK_CTL_CDR2_MASK + 1)) {
- if (div > 0)
- div--;
-
- reg = SUN6I_CLK_CTL_CDR2(div) | SUN6I_CLK_CTL_DRS;
+ div_cdr1 = DIV_ROUND_UP(mclk_rate, tfr->speed_hz);
+ div_cdr2 = DIV_ROUND_UP(div_cdr1, 2);
+ if (div_cdr2 <= (SUN6I_CLK_CTL_CDR2_MASK + 1)) {
+ reg = SUN6I_CLK_CTL_CDR2(div_cdr2 - 1) | SUN6I_CLK_CTL_DRS;
} else {
- div = ilog2(mclk_rate) - ilog2(tfr->speed_hz);
+ div = min(SUN6I_CLK_CTL_CDR1_MASK, order_base_2(div_cdr1));
reg = SUN6I_CLK_CTL_CDR1(div);
}
--
2.25.1
