Hi, On Tue, Jul 05, 2016 at 08:50:23AM +0200, Dirk Behme wrote: > 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. > > 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 > > too. > > To fix this, we will add the "unused" clocks in Xen to the hypervisor > node. The Linux kernel has to register the clocks from the hypervisor > node, then. > > Therefore, check if there is a "clocks" entry in the hypervisor node > and if so register the given clocks to the Linux kernel clock > framework and with this mark them as used. This prevents the clocks > from being disabled. > > Signed-off-by: Dirk Behme <dirk.behme@xxxxxxxxxxxx> > --- > Changes in v2: Drop the Linux implementation details like clk_disable_unused > in xen.txt. Thanks for doing this. > Documentation/devicetree/bindings/arm/xen.txt | 13 ++++++++ > arch/arm/xen/enlighten.c | 47 +++++++++++++++++++++++++++ > 2 files changed, 60 insertions(+) > > diff --git a/Documentation/devicetree/bindings/arm/xen.txt b/Documentation/devicetree/bindings/arm/xen.txt > index c9b9321..21fd469 100644 > --- a/Documentation/devicetree/bindings/arm/xen.txt > +++ b/Documentation/devicetree/bindings/arm/xen.txt > @@ -17,6 +17,19 @@ the following properties: > A GIC node is also required. > This property is unnecessary when booting Dom0 using ACPI. > > +Optional properties: > + > +- clocks: one or more clocks to be registered. > + Xen hypervisor drivers might replace native drivers, resulting in > + clocks not registered by these native drivers. To avoid that these > + unregistered clocks are disabled by the Linux kernel initialization > + register them in the hypervisor node. > + An example for this are the clocks of a serial driver already enabled > + by the firmware. If the clocks used by the serial hardware interface > + are not registered by the serial driver itself the serial output > + might stop once the Linux kernel initialization disables the 'unused' > + clocks. The above describes the set of problems, but doesn't set out the actual contract. It also covers a number of Linux implementation details in abstract. As I commented previously [1], the binding should describe the set of guarantees that you rewquire (e.g. that the clocks must be left as-is, not gated, and their rates left unchanged). Please describe the specific set of guarantees that you require. Thanks, Mark. [1] http://lists.infradead.org/pipermail/linux-arm-kernel/2016-June/440434.html -- 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
