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

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Thu, 14 Jul 2016, Dirk Behme wrote:
> On 13.07.2016 21:07, Stefano Stabellini wrote:
> > 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@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?
> > 
> > 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?
> 
> 
> With the recent code there is no global xen_node any more:
> 
> https://lists.xen.org/archives/html/xen-devel/2016-06/msg02878.html

Ops, I was looking at upstream. I forgot about those.

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