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

Dirk Behme
2016-07-13T18:47:16Z

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?

We need the xen_node from device tree, anyway.

Best regards

Dirk