Quoting Thierry Reding (2014-09-29 06:54:00) > On Mon, Sep 29, 2014 at 01:34:36PM +0200, Maxime Ripard wrote: > > On Mon, Sep 29, 2014 at 12:44:57PM +0200, Thierry Reding wrote: > > > > >> Plus, speaking more specifically about the clocks, that won't prevent > > > > >> your clock to be shut down as a side effect of a later clk_disable > > > > >> call from another driver. > > > > > > > > > Furthermore isn't it a bug for a driver to call clk_disable() before a > > > > > preceding clk_enable()? There are patches being worked on that will > > > > > enable per-user clocks and as I understand it they will specifically > > > > > disallow drivers to disable the hardware clock if other drivers are > > > > > still keeping them on via their own referenc. > > > > > > > > Calling clk_disable() preceding clk_enable() is a bug. > > > > > > > > Calling clk_disable() after clk_enable() will disable the clock (and > > > > its parents) > > > > if the clock subsystem thinks there are no other users, which is what will > > > > happen here. > > > > > > Right. I'm not sure this is really applicable to this situation, though. > > > > It's actually very easy to do. Have a driver that probes, enables its > > clock, fails to probe for any reason, call clk_disable in its exit > > path. If there's no other user at that time of this particular clock > > tree, it will be shut down. Bam. You just lost your framebuffer. > > > > Really, it's just that simple, and relying on the fact that some other > > user of the same clock tree will always be their is beyond fragile. > > Perhaps the meaning clk_ignore_unused should be revised, then. What you > describe isn't at all what I'd expect from such an option. And it does > not match the description in Documentation/kernel-parameters.txt either. >From e156ee56cbe26c9e8df6619dac1a993245afc1d5 Mon Sep 17 00:00:00 2001 From: Mike Turquette <mturquette@xxxxxxxxxx> Date: Tue, 30 Sep 2014 14:24:38 -0700 Subject: [PATCH] doc/kernel-parameters.txt: clarify clk_ignore_unused Refine the definition around clk_ignore_unused, which caused some confusion recently on the linux-fbdev and linux-arm-kernel mailing lists[0]. [0] http://lkml.kernel.org/r/<20140929135358.GC30998@ulmo> Signed-off-by: Mike Turquette <mturquette@xxxxxxxxxx> --- Thierry, Please let me know if this wording makes the feature more clear. Documentation/kernel-parameters.txt | 14 +++++++++----- 1 file changed, 9 insertions(+), 5 deletions(-) diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index 10d51c2..0ce01fb 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -605,11 +605,15 @@ bytes respectively. Such letter suffixes can also be entirely omitted. See Documentation/s390/CommonIO for details. clk_ignore_unused [CLK] - Keep all clocks already enabled by bootloader on, - even if no driver has claimed them. This is useful - for debug and development, but should not be - needed on a platform with proper driver support. - For more information, see Documentation/clk.txt. + Prevents the clock framework from automatically gating + clocks that have not been explicitly enabled by a Linux + device driver but are enabled in hardware at reset or + by the bootloader/firmware. Note that this does not + force such clocks to be always-on nor does it reserve + those clocks in any way. This parameter is useful for + debug and development, but should not be needed on a + platform with proper driver support. For more + information, see Documentation/clk.txt. clock= [BUGS=X86-32, HW] gettimeofday clocksource override. [Deprecated] -- 1.8.3.2 -- To unsubscribe from this list: send the line "unsubscribe linux-fbdev" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
