From mboxrd@z Thu Jan 1 00:00:00 1970 From: dirk.behme@gmail.com (Dirk Behme) Date: Wed, 13 Jul 2016 20:47:16 +0200 Subject: [Xen-devel] [PATCH v4] xen/arm: Add a clock property In-Reply-To: References: <1468309605-19522-1-git-send-email-dirk.behme@de.bosch.com> Message-ID: <57868CB4.1090504@gmail.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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 >> --- >> 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 >> #include >> #include >> +#include >> #include >> #include >> #include >> @@ -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