Generic Timer

The following are the requirements related to ARM Generic Timer [1] interface exposed by Xen to Arm64 domains.

Probe the Generic Timer device tree node from a domain

XenSwdgn~arm64_generic_timer_probe_dt~1

Description: Xen shall generate a device tree node for the Generic Timer (in accordance to ARM architected timer device tree binding [2]) in the domain device tree.

Rationale:

Comments: Domains can detect the presence of the Generic Timer device tree node.

Covers:

• XenProd~emulated_timer~1

Read system counter frequency

XenSwdgn~arm64_generic_timer_read_freq~1

Description: Xen shall expose the frequency of the system counter to the domains in CNTFRQ_EL0 register.

Rationale:

Comments:

Covers:

• XenProd~emulated_timer~1

Access CNTKCTL_EL1 system register from a domain

XenSwdgn~arm64_generic_timer_access_cntkctlel1~1

Description: Xen shall expose Counter-timer Kernel Control register (CNTKCTL_EL1) to the domains.

Rationale:

Comments:

Covers:

• XenProd~emulated_timer~1

Access virtual timer from a domain

XenSwdgn~arm64_generic_timer_access_virtual_timer~1

Description: Xen shall expose the virtual timer registers (CNTVCT_EL0, CNTV_CTL_EL0, CNTV_CVAL_EL0, CNTV_TVAL_EL0) to the domains.

Rationale:

Comments:

Covers:

• XenProd~emulated_timer~1

Access physical timer from a domain

XenSwdgn~arm64_generic_timer_access_physical_timer~1

Description: Xen shall expose physical timer registers (CNTPCT_EL0, CNTP_CTL_EL0, CNTP_CVAL_EL0, CNTP_TVAL_EL0) to the domains.

Rationale:

Comments:

Covers:

• XenProd~emulated_timer~1

Trigger the virtual timer interrupt from a domain

XenSwdgn~arm64_generic_timer_trigger_virtual_interrupt~1

Description: Xen shall generate virtual timer interrupts to domains when the virtual timer condition is met.

Rationale:

Comments:

Covers:

• XenProd~emulated_timer~1

Trigger the physical timer interrupt from a domain

XenSwdgn~arm64_generic_timer_trigger_physical_interrupt~1

Description: Xen shall generate physical timer interrupts to domains when the physical timer condition is met.

Rationale:

Comments:

Covers:

• XenProd~emulated_timer~1

Assumption of Use on the Platform

Expose system timer frequency via register

XenSwdgn~arm64_generic_timer_plat_program_cntfrq_el0~1

Description: CNTFRQ_EL0 register shall be programmed with the value of the system timer frequency.

Rationale: Xen reads the CNTFRQ_EL0 register to get the value of system timer frequency.

Comments: While there is a provision to get this value by reading the “clock-frequency” dt property [2], the use of this property is strongly discouraged.

Covers:

• XenProd~emulated_timer~1

[1] Arm Architecture Reference Manual for A-profile architecture, Chapter 11 [2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/timer/arm,arch_timer.yaml