armv8: implement workaround for broken CNTFRQ_EL0 value

In devices where the U-Boot is used as a secondary bootloader, we rely
on the device's primary bootloader to implement CNTFRQ_EL0. However,
this reliance may lead to a non-functional timer in broken firmware.

For instance, some versions of Samsung's S-Boot don't implement it. It's
also not possible to set it in the U-Boot, because it's booted in a lower
exception level. CNTFRQ_EL0 is reported to be 0.

Use gd->arch.timer_rate_hz to override the queried value if set. This
setting needs to be done in the board file, preferrably in timer_init().
This feature is present only when the CONFIG_ARMV8_CNTFRQ_BROKEN is
enabled.

Signed-off-by: Kaustabh Chakraborty <kauschluss@disroot.org>

diff --git a/arch/arm/cpu/armv8/Kconfig b/arch/arm/cpu/armv8/Kconfig
index 199335cd6040d30a355a7fd5448a449fa7f550fb..dfc4ce851c3a6e406423412b469164b2e6f7d5f8 100644 (file)
--- a/arch/arm/cpu/armv8/Kconfig
+++ b/arch/arm/cpu/armv8/Kconfig
@@ -4,6 +4,14 @@ config CMO_BY_VA_ONLY
        bool "Force cache maintenance to be exclusively by VA"
        depends on !SYS_DISABLE_DCACHE_OPS
 
+config ARMV8_CNTFRQ_BROKEN
+       bool "Fix broken ARMv8 generic timer"
+       depends on SYS_ARCH_TIMER
+       help
+         Say Y here if U-Boot depends on a prior stage bootloader, which
+         does not set the CNTFRQ_EL0 frequency, and its not possible to
+         set it from U-Boot either.
+
 config ARMV8_SPL_EXCEPTION_VECTORS
        bool "Install crash dump exception vectors"
        depends on SPL

diff --git a/arch/arm/cpu/armv8/generic_timer.c b/arch/arm/cpu/armv8/generic_timer.c
index 1de7ec596fc7cbbc3e78a241f163bc0a4fcad6b6..744ab3b91e59703ad83e19459e60a42643eb2e61 100644 (file)
--- a/arch/arm/cpu/armv8/generic_timer.c
+++ b/arch/arm/cpu/armv8/generic_timer.c
@@ -19,6 +19,10 @@ DECLARE_GLOBAL_DATA_PTR;
 unsigned long notrace get_tbclk(void)
 {
        unsigned long cntfrq;
+
+       if (IS_ENABLED(CONFIG_ARMV8_CNTFRQ_BROKEN) && gd->arch.timer_rate_hz)
+               return gd->arch.timer_rate_hz;
+
        asm volatile("mrs %0, cntfrq_el0" : "=r" (cntfrq));
        return cntfrq;
 }