From: Paul Walmsley <paul@xxxxxxxxx> Several parts of the OMAP2/3 clock code use wmb() to try to ensure that the hardware write completes before continuing. This approach is problematic: wmb() only ensures that the write leaves the ARM. It does not ensure that the write actually reaches the endpoint device. The endpoint device in this case - either the PRM, CM, or SCM - is three interconnects away from the ARM - and the final interconnect is low-speed. And the OCP interconnects will post the write, and who knows how long that will take to complete. So the wmb() is not what we want. Worse, the wmb() is indiscriminate; it causes the ARM to flush any other unrelated buffered writes and wait for the local interconnect to acknowledge them - potentially very expensive. Fix this by converting the wmb()s into readbacks of the same PRM/CM/SCM register. Since the PRM/CM/SCM devices use a single OCP thread, this will cause the MPU to block while waiting for posted writes to that device to complete. linux-omap source commit is 260f5487848681b4d8ea7430a709a601bbcb21d1. Signed-off-by: Paul Walmsley <paul@xxxxxxxxx> Signed-off-by: Tony Lindgren <tony@xxxxxxxxxxx> Signed-off-by: Russell King <rmk+kernel@xxxxxxxxxxxxxxxx> --- arch/arm/mach-omap2/clock.c | 6 +++--- 1 files changed, 3 insertions(+), 3 deletions(-) diff --git a/arch/arm/mach-omap2/clock.c b/arch/arm/mach-omap2/clock.c index 7f12230..666274a 100644 --- a/arch/arm/mach-omap2/clock.c +++ b/arch/arm/mach-omap2/clock.c @@ -334,7 +334,7 @@ static int omap2_dflt_clk_enable(struct clk *clk) else v |= (1 << clk->enable_bit); __raw_writel(v, clk->enable_reg); - wmb(); + v = __raw_readl(clk->enable_reg); /* OCP barrier */ return 0; } @@ -703,7 +703,7 @@ int omap2_clksel_set_rate(struct clk *clk, unsigned long rate) v &= ~clk->clksel_mask; v |= field_val << __ffs(clk->clksel_mask); __raw_writel(v, clk->clksel_reg); - wmb(); + v = __raw_readl(clk->clksel_reg); /* OCP barrier */ clk->rate = clk->parent->rate / new_div; @@ -788,7 +788,7 @@ int omap2_clk_set_parent(struct clk *clk, struct clk *new_parent) v &= ~clk->clksel_mask; v |= field_val << __ffs(clk->clksel_mask); __raw_writel(v, clk->clksel_reg); - wmb(); + v = __raw_readl(clk->clksel_reg); /* OCP barrier */ _omap2xxx_clk_commit(clk); -- 1.6.1.2 -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
