Commit 0f31932a authored by Flavio Suligoi's avatar Flavio Suligoi Committed by Greg Kroah-Hartman

spi: pxa2xx: fix SCR (divisor) calculation

[ Upstream commit 29f21337 ]

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: default avatarFlavio Suligoi <f.suligoi@asem.it>
Reviewed-by: default avatarJarkko Nikula <jarkko.nikula@linux.intel.com>
Reviewed-by: default avatarJarkko Nikula <jarkko.nikula@linux.intel.com>
Signed-off-by: default avatarMark Brown <broonie@kernel.org>
Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
parent 68f630d8
...@@ -921,10 +921,14 @@ static unsigned int ssp_get_clk_div(struct driver_data *drv_data, int rate) ...@@ -921,10 +921,14 @@ static unsigned int ssp_get_clk_div(struct driver_data *drv_data, int rate)
rate = min_t(int, ssp_clk, 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) 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 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, static unsigned int pxa2xx_ssp_get_clk_div(struct driver_data *drv_data,
......
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