Hi Simon On Wed, 21 Mar 2012, Simon Horman wrote: > This corrects an off-by one error when calculating the clock divisor. > The code previously assumed that for example a divisor of 2 is > set using a value of 0001 (the inverse of 1/2), a divisor of 4 is > set using a value of 0010 (the inverse of 1/4) etc.. However, the correct > values are 0000, 0001, etc... > > The use of DIV_ROUND_UP() was suggested by Guennadi Liakhovetski to avoid > understating the divisor by one in the case where the host clock is not a > binary power of the MMCIF clock. The patch looks good, but the commit message is not quite right. Cases of host->clk / clk != 2^n are handled by using fls(x - 1) instead of fls(x) - 1, as you initially suggested. DIV_ROUND_UP() is needed for divisions with a residue. E.g., for host clock 13MHz, target clock 3MHz you want a divisor of 5, resulting in 2 << 16, not 4, resulting in 1 << 16. With this fixed Acked-by: Guennadi Liakhovetski <g.liakhovetski@xxxxxx> Thanks Guennadi > > Cc: Guennadi Liakhovetski <g.liakhovetski@xxxxxx> > Tested-by: Cao Minh Hiep <hiepcm@xxxxxxxxx> > Signed-off-by: Simon Horman <horms@xxxxxxxxxxxx> > --- > drivers/mmc/host/sh_mmcif.c | 3 ++- > 1 files changed, 2 insertions(+), 1 deletions(-) > > diff --git a/drivers/mmc/host/sh_mmcif.c b/drivers/mmc/host/sh_mmcif.c > index 8057bf3..5014bc4 100644 > --- a/drivers/mmc/host/sh_mmcif.c > +++ b/drivers/mmc/host/sh_mmcif.c > @@ -453,7 +453,8 @@ static void sh_mmcif_clock_control(struct sh_mmcif_host *host, unsigned int clk) > sh_mmcif_bitset(host, MMCIF_CE_CLK_CTRL, CLK_SUP_PCLK); > else > sh_mmcif_bitset(host, MMCIF_CE_CLK_CTRL, CLK_CLEAR & > - ((fls(host->clk / clk) - 1) << 16)); > + ((fls(DIV_ROUND_UP(host->clk, > + clk) - 1) - 1) << 16)); > > sh_mmcif_bitset(host, MMCIF_CE_CLK_CTRL, CLK_ENABLE); > } > -- > 1.7.6.3 > --- Guennadi Liakhovetski, Ph.D. Freelance Open-Source Software Developer http://www.open-technology.de/ -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
