On 13.07.2016 23:03, Michael Turquette wrote:
Quoting Dirk Behme (2016-07-13 11:56:30)
On 13.07.2016 20:43, Stefano Stabellini wrote:
On Wed, 13 Jul 2016, Dirk Behme wrote:
On 13.07.2016 00:26, Michael Turquette wrote:
Quoting Dirk Behme (2016-07-12 00:46:45)
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 that clk_prepare_enable will not prevent the rate from changing
(clk_set_rate) or a parent from changing (clk_set_parent). The only way
to do this currently would be to set the following flags on the effected
clocks:
CLK_SET_RATE_GATE
CLK_SET_PARENT_GATE
Regarding setting flags, I think we already talked about that. I think the
conclusion was that in our case its not possible to manipulate the flags in
the OS as this isn't intended to be done in cases like ours. Therefore no API
is exported for this.
I.e. if we need to set these flags, we have to do that in Xen where we add the
clocks to the hypervisor node in the device tree. And not in the kernel patch
discussed here.
These are internal Linux flags, aren't they?
I've been under the impression that you can set clock "flags" via the
device tree. Seems I need to re-check that ;)
Right, you cannot set flags from the device tree. Also, setting these
flags is done by the clock provider driver, not a consumer. Xen is the
consumer.
Ok, thanks, then I think we can forget about using flags for the issue
we are discussing here.
Best regards
Dirk
P.S.: Would it be an option to merge the v4 patch we are discussing
here, then? From the discussion until here, it sounds to me that it's
the best option we have at the moment. Maybe improving it in the future,
then.
They cannot be set in Xen.
If the only way to make sure that clk_set_rate and clk_set_parent fail
on one of the clocks "owned" by Xen is to set CLK_SET_RATE_GATE and
CLK_SET_PARENT_GATE, we'll have to do that. Even if it means introducing
a new internal Linux API.
And then enable the clocks. All calls to clk_set_parent and clk_set_rate
with those clocks in the path will fail, so long as they are prepared
and enabled. This implementation detail is specific to Linux and
definitely should not go into the binding.
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.
I'm still not completely sure about this type of layering and whether or
not it is sane. If you want Xen to manage the clock controller, AND you
want Linux guests or dom0 to consume those clocks and manipulate them in
other drivers, then this solution won't work.
Regards,
Mike
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;
+ }
+
+ count = of_clk_get_parent_count(xen_node);
+ if (!count)
+ goto out;
+
+ for (i = 0; i < count; i++) {
+ clk = of_clk_get(xen_node, i);
+ if (IS_ERR(clk)) {
+ pr_err("Xen failed to register clock %i. Error:
%li\n",
+ i, PTR_ERR(clk));
+ ret = PTR_ERR(clk);
+ goto out;
+ }
+
+ ret = clk_prepare_enable(clk);
+ if (ret < 0) {
+ pr_err("Xen failed to enable clock %i. Error:
%i\n",
+ i, ret);
+ goto out;
+ }
+ }
+
+ ret = 0;
+
+out:
+ of_node_put(xen_node);
+ return ret;
+}
+late_initcall(xen_arm_register_clks);
/* empty stubs */
void xen_arch_pre_suspend(void) { }
--
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