Hi Saravana, On Fri, May 11, 2012 at 09:59:56PM -0700, Saravana Kannan wrote: > Without this patch, the following race conditions are possible. > > Race condition 1: > * clk-A has two parents - clk-X and clk-Y. > * All three are disabled and clk-X is current parent. > * Thread A: clk_set_parent(clk-A, clk-Y). > * Thread A: <snip execution flow> > * Thread A: Grabs enable lock. > * Thread A: Sees enable count of clk-A is 0, so doesn't enable clk-Y. > * Thread A: Releases enable lock. > * Thread B: Calls clk_enable(clk-A), which in turn enables clk-X. > * Thread A: Switches clk-A's parent to clk-Y in hardware. > > clk-A is now enabled in software, but not clocking in hardware. > > Race condition 2: > * clk-A has two parents - clk-X and clk-Y. > * All three are disabled and clk-X is current parent. > * Thread A: clk_set_parent(clk-A, clk-Y). > * Thread A: <snip execution flow> > * Thread A: Switches parent in hardware to clk-Y. > * Thread A: Grabs enable lock. > * Thread A: Sees enable count of clk-A is 0, so doesn't disable clk-X. > * Thread A: Releases enable lock. > * Thread B: Calls clk_enable(clk-A) > * Thread B: Software state still says parent is clk-X. > * Thread B: So, enables clk-X and then itself. > * Thread A: Updates parent in software state to clk-Y. Had a look at this and I can follow your reasoning and you patch seems to fix this. However, there is a problem, > > /* migrate prepare and enable */ > @@ -1092,23 +1098,23 @@ static int __clk_set_parent(struct clk *clk, struct clk *parent) > > /* FIXME replace with clk_is_enabled(clk) someday */ > spin_lock_irqsave(&enable_lock, flags); > + > if (clk->enable_count) > __clk_enable(parent); > - spin_unlock_irqrestore(&enable_lock, flags); > > /* change clock input source */ > ret = clk->ops->set_parent(clk->hw, i); You call ->set_parent while holding a spinlock. This won't work with i2c clocks. Sascha -- Pengutronix e.K. | | Industrial Linux Solutions | http://www.pengutronix.de/ | Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 | -- To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
