Hi Julien, Quoting Julien Grall (2016-07-06 06:10:52) > On 06/07/16 02:34, Michael Turquette wrote: > > Hi! > > Hello Michael, > > > Quoting Dirk Behme (2016-06-30 03:32:32) > >> Some clocks might be used by the Xen hypervisor and not by the Linux > >> kernel. If these are not registered by the Linux kernel, they might be > >> disabled by clk_disable_unused() as the kernel doesn't know that they > >> are used. The clock of the serial console handled by Xen is one > >> example for this. It might be disabled by clk_disable_unused() which > >> stops the whole serial output, even from Xen, then. > > > > This whole thread had me confused until I realized that it all boiled > > down to some nomenclature issues (for me). > > > > This code does not _register_ any clocks. It simply gets them and > > enables them, which is what every other clk consumer in the Linux kernel > > does. More details below. > > > >> > >> Up to now, the workaround for this has been to use the Linux kernel > >> command line parameter 'clk_ignore_unused'. See Xen bug > >> > >> http://bugs.xenproject.org/xen/bug/45 > > > > clk_ignore_unused is a band-aid, not a proper medical solution. Setting > > that flag will not turn clocks on for you, nor will it guarantee that > > those clocks are never turned off in the future. It looks like you > > figured this out correctly in the patch below but it is worth repeating. > > > > Also the new CLK_IS_CRITICAL flag might be of interest to you, but that > > flag only exists as a way to enable clocks that must be enabled for the > > system to function (hence, "critical") AND when those same clocks do not > > have an accompanying Linux driver to consume them and enable them. > > I don't think we want the kernel to enable the clock for the hypervisor. > We want to tell the kernel "don't touch at all to this clock, it does > not belong to you". But the patch *does* touch the clock from the kernel. It enables the clock via a call clk_prepare_enable. I'm utterly confused. Regards, Mike > > Regards, > > -- > Julien Grall -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
