From e689d6df8257f92abf59e93736632b79c9b2aa66 Mon Sep 17 00:00:00 2001 From: Aaron Brice Date: Fri, 3 Apr 2015 13:39:29 -0700 Subject: [PATCH] spi: fsl-dspi: Fix clock rate scale values Previous algorithm had an outer loop with the values {2,3,5,7} and an inner loop with {2,4,6,8,16,32,...,32768}, and would pick the first value over the required scaling value (where the total scale was the two numbers multiplied). Since the inner loop went up to 32768 it would always pick a value of 2 for PBR and a much higher than necessary value for BR. The desired scale factor was being divided by two I believe to compensate for the much higher scale factors (the divide by two not specified in the reference manual). Updated to check all values and find the smallest scale factor possible without going over the desired clock rate. Signed-off-by: Aaron Brice Signed-off-by: Mark Brown --- drivers/spi/spi-fsl-dspi.c | 37 +++++++++++++++++++++++-------------- 1 file changed, 23 insertions(+), 14 deletions(-) diff --git a/drivers/spi/spi-fsl-dspi.c b/drivers/spi/spi-fsl-dspi.c index d1a39249704a..82133584c0ea 100644 --- a/drivers/spi/spi-fsl-dspi.c +++ b/drivers/spi/spi-fsl-dspi.c @@ -148,23 +148,32 @@ static void hz_to_spi_baud(char *pbr, char *br, int speed_hz, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192, 16384, 32768 }; - int temp, i = 0, j = 0; - - temp = clkrate / 2 / speed_hz; - - for (i = 0; i < ARRAY_SIZE(pbr_tbl); i++) - for (j = 0; j < ARRAY_SIZE(brs); j++) { - if (pbr_tbl[i] * brs[j] >= temp) { - *pbr = i; - *br = j; - return; + int scale_needed, scale, minscale = INT_MAX; + int i, j; + + scale_needed = clkrate / speed_hz; + if (clkrate % speed_hz) + scale_needed++; + + for (i = 0; i < ARRAY_SIZE(brs); i++) + for (j = 0; j < ARRAY_SIZE(pbr_tbl); j++) { + scale = brs[i] * pbr_tbl[j]; + if (scale >= scale_needed) { + if (scale < minscale) { + minscale = scale; + *br = i; + *pbr = j; + } + break; } } - pr_warn("Can not find valid baud rate,speed_hz is %d,clkrate is %ld\ - ,we use the max prescaler value.\n", speed_hz, clkrate); - *pbr = ARRAY_SIZE(pbr_tbl) - 1; - *br = ARRAY_SIZE(brs) - 1; + if (minscale == INT_MAX) { + pr_warn("Can not find valid baud rate,speed_hz is %d,clkrate is %ld, we use the max prescaler value.\n", + speed_hz, clkrate); + *pbr = ARRAY_SIZE(pbr_tbl) - 1; + *br = ARRAY_SIZE(brs) - 1; + } } static int dspi_transfer_write(struct fsl_dspi *dspi) -- 2.20.1