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

Dirk Behme
2016-07-14T06:11:16Z

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@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?

With the recent code there is no global xen_node any more:

https://lists.xen.org/archives/html/xen-devel/2016-06/msg02878.html

-- cut --
The code in this file has changed quite a lot with the support of ACPI.
For instance "xen_node" is not anymore a global variable. Can you rebase
your rework on top of the branch for-linus-4.8?

You can find the branch in:

git://git.kernel.org/pub/scm/linux/kernel/git/xen/tip.git
-- cut --

Best regards

Dirk