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

[Stefano Stabellini <sstabellini@kernel.org>]

On Wed, 13 Jul 2016, Dirk Behme wrote:
> 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@de.bosch.com>
> > > ---
> > > 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?

As a Xen check, if (!xen_domain()) is the common pattern.

> We need the xen_node from device tree, anyway.

In that case, what don't you just use the global xen_node in this file?