mmc: sdhci-s3c: Use shifts to divide by powers of two

Current implementation of sdhci_s3c_consider_clock() is highly
inefficient due to multiple integer divisions by variable performed in a
loop. Since only divisors that are powers of two are considered, this
patch replaces them with respective shifts, removing all the integer
divisions.

Signed-off-by: Tomasz Figa <tomasz.figa@gmail.com>
Tested-by: Heiko Stuebner <heiko@sntech.de>
Acked-by: Heiko Stuebner <heiko@sntech.de>
Tested-by: Jaehoon Chung <jh80.chung@samsung.com>
Acked-by; Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Chris Ball <chris@printf.net>

diff --git a/drivers/mmc/host/sdhci-s3c.c b/drivers/mmc/host/sdhci-s3c.c
index 6debda9..52770d5 100644 (file)
--- a/drivers/mmc/host/sdhci-s3c.c
+++ b/drivers/mmc/host/sdhci-s3c.c
@@ -144,7 +144,7 @@ static unsigned int sdhci_s3c_consider_clock(struct sdhci_s3c *ourhost,
 {
        unsigned long rate;
        struct clk *clksrc = ourhost->clk_bus[src];
-       int div;
+       int shift;
 
        if (!clksrc)
                return UINT_MAX;
@@ -160,15 +160,15 @@ static unsigned int sdhci_s3c_consider_clock(struct sdhci_s3c *ourhost,
 
        rate = clk_get_rate(clksrc);
 
-       for (div = 1; div < 256; div *= 2) {
-               if ((rate / div) <= wanted)
+       for (shift = 0; shift < 8; ++shift) {
+               if ((rate >> shift) <= wanted)
                        break;
        }
 
        dev_dbg(&ourhost->pdev->dev, "clk %d: rate %ld, want %d, got %ld\n",
-               src, rate, wanted, rate / div);
+               src, rate, wanted, rate >> shift);
 
-       return wanted - (rate / div);
+       return wanted - (rate >> shift);
 }
 
 /**