On Wed, 13 Jul 2016, Dirk Behme wrote: > On 13.07.2016 00:26, Michael Turquette wrote: > > Quoting Dirk Behme (2016-07-12 00:46:45) > > > Clocks described by this property are reserved for use by Xen, and the OS > > > must not alter their state any way, such as disabling or gating a clock, > > > or modifying its rate. Ensuring this may impose constraints on parent > > > clocks or other resources used by the clock tree. > > > > Note that clk_prepare_enable will not prevent the rate from changing > > (clk_set_rate) or a parent from changing (clk_set_parent). The only way > > to do this currently would be to set the following flags on the effected > > clocks: > > > > CLK_SET_RATE_GATE > > CLK_SET_PARENT_GATE > > > > Regarding setting flags, I think we already talked about that. I think the > conclusion was that in our case its not possible to manipulate the flags in > the OS as this isn't intended to be done in cases like ours. Therefore no API > is exported for this. > > I.e. if we need to set these flags, we have to do that in Xen where we add the > clocks to the hypervisor node in the device tree. And not in the kernel patch > discussed here. These are internal Linux flags, aren't they? They cannot be set in Xen. If the only way to make sure that clk_set_rate and clk_set_parent fail on one of the clocks "owned" by Xen is to set CLK_SET_RATE_GATE and CLK_SET_PARENT_GATE, we'll have to do that. Even if it means introducing a new internal Linux API. > > And then enable the clocks. All calls to clk_set_parent and clk_set_rate > > with those clocks in the path will fail, so long as they are prepared > > and enabled. This implementation detail is specific to Linux and > > definitely should not go into the binding. > > > > > > > > This property is used to proxy clocks for devices Xen has taken ownership > > > of, such as UARTs, for which the associated clock controller(s) remain > > > under the control of Dom0. > > > > I'm still not completely sure about this type of layering and whether or > > not it is sane. If you want Xen to manage the clock controller, AND you > > want Linux guests or dom0 to consume those clocks and manipulate them in > > other drivers, then this solution won't work. > > > > Regards, > > Mike > > > > > > > > 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. > > > > > > Signed-off-by: Dirk Behme <dirk.behme@xxxxxxxxxxxx> > > > --- > > > Changes in v4: Switch to the xen.txt description proposed by Mark: > > > https://www.spinics.net/lists/arm-kernel/msg516158.html > > > > > > Changes in v3: Use the xen.txt description proposed by Michael. Thanks! > > > > > > Changes in v2: Drop the Linux implementation details like > > > clk_disable_unused > > > in xen.txt. > > > > > > Documentation/devicetree/bindings/arm/xen.txt | 12 +++++++ > > > arch/arm/xen/enlighten.c | 47 > > > +++++++++++++++++++++++++++ > > > 2 files changed, 59 insertions(+) > > > > > > diff --git a/Documentation/devicetree/bindings/arm/xen.txt > > > b/Documentation/devicetree/bindings/arm/xen.txt > > > index c9b9321..437e50b 100644 > > > --- a/Documentation/devicetree/bindings/arm/xen.txt > > > +++ b/Documentation/devicetree/bindings/arm/xen.txt > > > @@ -17,6 +17,18 @@ the following properties: > > > A GIC node is also required. > > > This property is unnecessary when booting Dom0 using ACPI. > > > > > > +Optional properties: > > > + > > > +- clocks: a list of phandle + clock-specifier pairs > > > + Clocks described by this property are reserved for use by Xen, and the > > > + OS must not alter their state any way, such as disabling or gating a > > > + clock, or modifying its rate. Ensuring this may impose constraints on > > > + parent clocks or other resources used by the clock tree. > > > + > > > + Note: this property is used to proxy clocks for devices Xen has taken > > > + ownership of, such as UARTs, for which the associated clock > > > + controller(s) remain under the control of Dom0. > > > + > > > 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) { } > > > -- > -- 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
