path: root/arch/powerpc/platforms
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authorGerhard Sittig <gsi@denx.de>2013-12-10 13:11:35 (GMT)
committerAnatolij Gustschin <agust@denx.de>2014-01-12 17:59:21 (GMT)
commit76922ebb02fb531142285682352ccdd7091a2bfb (patch)
treea0778868b3fea328d5a7b4bb975911dc71d022a5 /arch/powerpc/platforms
parent2a2b9ff8a544944ee97b80b9ff977986c9e05e7f (diff)
powerpc/512x: clk: enforce even SDHC divider values
the SDHC clock is derived from CSB with a fractional divider which can address "quarters"; the implementation multiplies CSB by 4 and divides it by the (integer) divider value a bug in the clock domain synchronisation requires that only even divider values get setup; we achieve this by - multiplying CSB by 2 only instead of 4 - registering with CCF the divider's bit field without bit0 - the divider's lowest bit remains clear as this is the reset value and later operations won't touch it this change keeps fully utilizing common clock primitives (needs no additional support logic, and avoids an excessive divider table) and satisfies the hardware's constraint of only supporting even divider values Signed-off-by: Gerhard Sittig <gsi@denx.de> Acked-by: Mike Turquette <mturquette@linaro.org> Signed-off-by: Anatolij Gustschin <agust@denx.de>
Diffstat (limited to 'arch/powerpc/platforms')
1 files changed, 14 insertions, 2 deletions
diff --git a/arch/powerpc/platforms/512x/clock-commonclk.c b/arch/powerpc/platforms/512x/clock-commonclk.c
index a97ce88..1656937 100644
--- a/arch/powerpc/platforms/512x/clock-commonclk.c
+++ b/arch/powerpc/platforms/512x/clock-commonclk.c
@@ -560,9 +560,21 @@ static void mpc512x_clk_setup_clock_tree(struct device_node *np, int busfreq)
/* now setup anything below SYS and CSB and IPS */
clks[MPC512x_CLK_DDR_UG] = mpc512x_clk_factor("ddr-ug", "sys", 1, 2);
- clks[MPC512x_CLK_SDHC_x4] = mpc512x_clk_factor("sdhc-x4", "csb", 4, 1);
+ /*
+ * the Reference Manual discusses that for SDHC only even divide
+ * ratios are supported because clock domain synchronization
+ * between 'per' and 'ipg' is broken;
+ * keep the divider's bit 0 cleared (per reset value), and only
+ * allow to setup the divider's bits 7:1, which results in that
+ * only even divide ratios can get configured upon rate changes;
+ * keep the "x4" name because this bit shift hack is an internal
+ * implementation detail, the "fractional divider with quarters"
+ * semantics remains
+ */
+ clks[MPC512x_CLK_SDHC_x4] = mpc512x_clk_factor("sdhc-x4", "csb", 2, 1);
clks[MPC512x_CLK_SDHC_UG] = mpc512x_clk_divider("sdhc-ug", "sdhc-x4", 0,
- &clkregs->scfr2, 0, 8,
+ &clkregs->scfr2, 1, 7,
clks[MPC512x_CLK_DIU_x4] = mpc512x_clk_factor("diu-x4", "csb", 4, 1);
clks[MPC512x_CLK_DIU_UG] = mpc512x_clk_divider("diu-ug", "diu-x4", 0,

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