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mmc: sunxi: Fix clock frequency change sequence 

The SD specification documents that the clock frequency should only be
changed once gated (Section 3.2.3 - SD Clock Frequency Change Sequence).

The current code first modifies the parent clock, gates it and then
modifies the internal divider. This means that since the parent clock rate
might be changed, the bus clock might be changed as well before it is
gated, which breaks the specification.

Move the gating before the parent rate modification.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Tested-by: Florian Vaussard <florian.vaussard@heig-vd.ch>
Acked-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
This commit is contained in:
Maxime Ripard 2017-01-27 22:38:33 +01:00 committed by Ulf Hansson
parent 1ed2171944
commit 39cc281fb7
1 changed files with 4 additions and 4 deletions
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8
drivers/mmc/host/sunxi-mmc.c
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@ -761,6 +761,10 @@ static int sunxi_mmc_clk_set_rate(struct sunxi_mmc_host *host,
u32 rval, clock = ios->clock;
int ret;
ret = sunxi_mmc_oclk_onoff(host, 0);
if (ret)
return ret;
/* 8 bit DDR requires a higher module clock */
if (ios->timing == MMC_TIMING_MMC_DDR52 &&
ios->bus_width == MMC_BUS_WIDTH_8)
@ -783,10 +787,6 @@ static int sunxi_mmc_clk_set_rate(struct sunxi_mmc_host *host,
return ret;
}
ret = sunxi_mmc_oclk_onoff(host, 0);
if (ret)
return ret;
/* clear internal divider */
rval = mmc_readl(host, REG_CLKCR);
rval &= ~0xff;