From 29f2133717c527f492933b0622a4aafe0b3cbe9e Mon Sep 17 00:00:00 2001
From: Flavio Suligoi <f.suligoi@asem.it>
Date: Fri, 12 Apr 2019 09:32:19 +0200
Subject: [PATCH] spi: pxa2xx: fix SCR (divisor) calculation
Git-commit: 29f2133717c527f492933b0622a4aafe0b3cbe9e
Patch-mainline: v5.2-rc1
References: bsc#1051510
Calculate the divisor for the SCR (Serial Clock Rate), avoiding
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@asem.it>
Reviewed-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Acked-by: Takashi Iwai <tiwai@suse.de>
---
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 b6ddba833d02..d2076f2f468f 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;
}
static unsigned int pxa2xx_ssp_get_clk_div(struct driver_data *drv_data,
--
2.16.4