Re: [Xen-devel] [PATCH v4] xen/arm: Add a clock property

[Dirk Behme <dirk.behme@xxxxxxxxx>]

On 13.07.2016 20:35, Stefano Stabellini wrote:
> On Tue, 12 Jul 2016, Dirk Behme wrote:
> > 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.
> >
> > 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.
> >
> > 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;
> > +       }
> Given that this is a late initcall, the following should work:
>
>      if (!xen_domain())
>          return -ENODEV;

Hmm, sorry, "should work" for what?

We need the xen_node from device tree, anyway.

Best regards

Dirk


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