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The ARM Generic Timer (AKA the architected timer, arm_arch_timer) features a CPU register (CNTFRQ) which firmware is intended to initialize, and non-secure software can read to determine the frequency of the timer. On CPUs with secure state, this register cannot be written from non-secure states. The firmware of early SoCs featuring the timer did not correctly initialize CNTFRQ correctly on all CPUs, requiring the frequency to be described in DT as a workaround. This workaround is not complete however as it is exposed to all software in a privileged non-secure mode (including guests running under a hypervisor). The firmware and DTs for recent SoCs have followed the example set by these early SoCs. This patch updates the arch timer binding documentation to make it clearer that the use of the clock-frequency property is a poor work-around. The MMIO generic timer binding is similarly updated, though this is less of a concern as there is generally no need to expose the MMIO timers to guest OSs. Signed-off-by: Mark Rutland <mark.rutland@arm.com> Acked-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Marc Zyngier <marc.zyngier@arm.com> Acked-by: Olof Johansson <olof@lixom.net> Acked-by: Stephen Boyd <sboyd@codeaurora.org> Cc: Rob Herring <robh+dt@kernel.org> Cc: Will Deacon <will.deacon@arm.com> Signed-off-by: Rob Herring <robh@kernel.org>
97 lines
2.8 KiB
Plaintext
97 lines
2.8 KiB
Plaintext
* ARM architected timer
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ARM cores may have a per-core architected timer, which provides per-cpu timers,
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or a memory mapped architected timer, which provides up to 8 frames with a
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physical and optional virtual timer per frame.
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The per-core architected timer is attached to a GIC to deliver its
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per-processor interrupts via PPIs. The memory mapped timer is attached to a GIC
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to deliver its interrupts via SPIs.
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** CP15 Timer node properties:
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- compatible : Should at least contain one of
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"arm,armv7-timer"
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"arm,armv8-timer"
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- interrupts : Interrupt list for secure, non-secure, virtual and
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hypervisor timers, in that order.
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- clock-frequency : The frequency of the main counter, in Hz. Should be present
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only where necessary to work around broken firmware which does not configure
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CNTFRQ on all CPUs to a uniform correct value. Use of this property is
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strongly discouraged; fix your firmware unless absolutely impossible.
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- always-on : a boolean property. If present, the timer is powered through an
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always-on power domain, therefore it never loses context.
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** Optional properties:
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- arm,cpu-registers-not-fw-configured : Firmware does not initialize
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any of the generic timer CPU registers, which contain their
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architecturally-defined reset values. Only supported for 32-bit
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systems which follow the ARMv7 architected reset values.
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Example:
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timer {
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compatible = "arm,cortex-a15-timer",
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"arm,armv7-timer";
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interrupts = <1 13 0xf08>,
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<1 14 0xf08>,
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<1 11 0xf08>,
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<1 10 0xf08>;
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clock-frequency = <100000000>;
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};
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** Memory mapped timer node properties:
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- compatible : Should at least contain "arm,armv7-timer-mem".
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- clock-frequency : The frequency of the main counter, in Hz. Should be present
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only when firmware has not configured the MMIO CNTFRQ registers.
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- reg : The control frame base address.
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Note that #address-cells, #size-cells, and ranges shall be present to ensure
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the CPU can address a frame's registers.
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A timer node has up to 8 frame sub-nodes, each with the following properties:
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- frame-number: 0 to 7.
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- interrupts : Interrupt list for physical and virtual timers in that order.
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The virtual timer interrupt is optional.
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- reg : The first and second view base addresses in that order. The second view
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base address is optional.
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- status : "disabled" indicates the frame is not available for use. Optional.
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Example:
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timer@f0000000 {
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compatible = "arm,armv7-timer-mem";
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#address-cells = <1>;
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#size-cells = <1>;
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ranges;
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reg = <0xf0000000 0x1000>;
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clock-frequency = <50000000>;
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frame@f0001000 {
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frame-number = <0>
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interrupts = <0 13 0x8>,
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<0 14 0x8>;
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reg = <0xf0001000 0x1000>,
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<0xf0002000 0x1000>;
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};
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frame@f0003000 {
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frame-number = <1>
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interrupts = <0 15 0x8>;
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reg = <0xf0003000 0x1000>;
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status = "disabled";
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};
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};
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