On Thu, 30 Jun 2016, 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: > - Rebase against git://git.kernel.org/pub/scm/linux/kernel/git/xen/tip.git for-linus-4.8 > - Add changes to Documentation/devicetree/bindings/arm/xen.txt > > Documentation/devicetree/bindings/arm/xen.txt | 11 +++++++ > arch/arm/xen/enlighten.c | 47 +++++++++++++++++++++++++++ > 2 files changed, 58 insertions(+) > > diff --git a/Documentation/devicetree/bindings/arm/xen.txt b/Documentation/devicetree/bindings/arm/xen.txt > index c9b9321..55dfd3b 100644 > --- a/Documentation/devicetree/bindings/arm/xen.txt > +++ b/Documentation/devicetree/bindings/arm/xen.txt > @@ -17,6 +17,17 @@ 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, then, e.g. by clk_disable_unused(), > + register them in the hypervisor node. > + An example for this are the clocks of the serial driver. If the clocks > + used by the serial hardware interface are not registered by the serial > + driver the serial output might stop once clk_disable_unused() is called. What if we use the "status" property of the clocks? Could we set it to "disabled" in Xen? Would that be enough for Linux to leave them alone? > To support UEFI on Xen ARM virtual platforms, Xen populates the FDT "uefi" node > under /hypervisor with following parameters: > > diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c > index 47acb36..5c546d0 100644 > --- a/arch/arm/xen/enlighten.c > +++ b/arch/arm/xen/enlighten.c > @@ -24,6 +24,7 @@ > #include <linux/of_fdt.h> > #include <linux/of_irq.h> > #include <linux/of_address.h> > +#include <linux/clk-provider.h> > #include <linux/cpuidle.h> > #include <linux/cpufreq.h> > #include <linux/cpu.h> > @@ -444,6 +445,52 @@ static int __init xen_pm_init(void) > } > late_initcall(xen_pm_init); > > +/* > + * Check if we want to register some clocks, that they > + * are not freed because unused by clk_disable_unused(). > + * E.g. the serial console clock. > + */ > +static int __init xen_arm_register_clks(void) > +{ > + struct clk *clk; > + struct device_node *xen_node; > + unsigned int i, count; > + int ret = 0; > + > + xen_node = of_find_compatible_node(NULL, NULL, "xen,xen"); > + if (!xen_node) { > + pr_err("Xen support was detected before, but it has disappeared\n"); > + return -EINVAL; > + } > + > + count = of_clk_get_parent_count(xen_node); > + if (!count) > + goto out; > + > + for (i = 0; i < count; i++) { > + clk = of_clk_get(xen_node, i); > + if (IS_ERR(clk)) { > + pr_err("Xen failed to register clock %i. Error: %li\n", > + i, PTR_ERR(clk)); > + ret = PTR_ERR(clk); > + goto out; > + } > + > + ret = clk_prepare_enable(clk); > + if (ret < 0) { > + pr_err("Xen failed to enable clock %i. Error: %i\n", > + i, ret); > + goto out; > + } > + } > + > + ret = 0; > + > +out: > + of_node_put(xen_node); > + return ret; > +} > +late_initcall(xen_arm_register_clks); > > /* empty stubs */ > void xen_arch_pre_suspend(void) { } > -- > 2.8.0 > -- 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
