[U-Boot] [PATCH v4 02/12] x86: Allow a hardcoded TSC frequency provided by Kconfig

[Bin Meng]

By default U-Boot automatically calibrates TSC running frequency via
MSR and PIT. The calibration may not work on every x86 processor, so
a new Kconfig option CONFIG_TSC_CALIBRATION_BYPASS is introduced to
allow bypassing the calibration and assign a hardcoded TSC frequency
CONFIG_TSC_FREQ_IN_MHZ.

Normally the bypass should be turned on in a simulation environment
like qemu.

Signed-off-by: Bin Meng <bmeng.cn at gmail.com>
Acked-by: Simon Glass <sjg at chromium.org>

---

Changes in v4: None
Changes in v3: None
Changes in v2:
- Spell out TSC, MSR and PIT in the Kconfig help

 arch/x86/Kconfig         | 20 ++++++++++++++++++++
 arch/x86/lib/tsc_timer.c |  8 ++++++--
 2 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index e992e64..ffcb4cb 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -313,6 +313,26 @@ config FRAMEBUFFER_VESA_MODE
 
 endmenu
 
+config TSC_CALIBRATION_BYPASS
+	bool "Bypass Time-Stamp Counter (TSC) calibration"
+	default n
+	help
+	  By default U-Boot automatically calibrates Time-Stamp Counter (TSC)
+	  running frequency via Model-Specific Register (MSR) and Programmable
+	  Interval Timer (PIT). If the calibration does not work on your board,
+	  select this option and provide a hardcoded TSC running frequency with
+	  CONFIG_TSC_FREQ_IN_MHZ below.
+
+	  Normally this option should be turned on in a simulation environment
+	  like qemu.
+
+config TSC_FREQ_IN_MHZ
+	int "Time-Stamp Counter (TSC) running frequency in MHz"
+	depends on TSC_CALIBRATION_BYPASS
+	default 1000
+	help
+	  The running frequency in MHz of Time-Stamp Counter (TSC).
+
 source "arch/x86/cpu/ivybridge/Kconfig"
 
 source "arch/x86/cpu/queensbay/Kconfig"
diff --git a/arch/x86/lib/tsc_timer.c b/arch/x86/lib/tsc_timer.c
index fb9afed..7f5ba2c 100644
--- a/arch/x86/lib/tsc_timer.c
+++ b/arch/x86/lib/tsc_timer.c
@@ -78,7 +78,7 @@ static int match_cpu(u8 family, u8 model)
  *
  * Returns the calibration value or 0 if MSR calibration failed.
  */
-static unsigned long try_msr_calibrate_tsc(void)
+static unsigned long __maybe_unused try_msr_calibrate_tsc(void)
 {
 	u32 lo, hi, ratio, freq_id, freq;
 	unsigned long res;
@@ -199,7 +199,7 @@ static inline int pit_expect_msb(unsigned char val, u64 *tscp,
 #define MAX_QUICK_PIT_MS 50
 #define MAX_QUICK_PIT_ITERATIONS (MAX_QUICK_PIT_MS * PIT_TICK_RATE / 1000 / 256)
 
-static unsigned long quick_pit_calibrate(void)
+static unsigned long __maybe_unused quick_pit_calibrate(void)
 {
 	int i;
 	u64 tsc, delta;
@@ -306,6 +306,9 @@ unsigned __attribute__((no_instrument_function)) long get_tbclk_mhz(void)
 	if (gd->arch.tsc_mhz)
 		return gd->arch.tsc_mhz;
 
+#ifdef CONFIG_TSC_CALIBRATION_BYPASS
+	fast_calibrate = CONFIG_TSC_FREQ_IN_MHZ;
+#else
 	fast_calibrate = try_msr_calibrate_tsc();
 	if (!fast_calibrate) {
 
@@ -313,6 +316,7 @@ unsigned __attribute__((no_instrument_function)) long get_tbclk_mhz(void)
 		if (!fast_calibrate)
 			panic("TSC frequency is ZERO");
 	}
+#endif
 
 	gd->arch.tsc_mhz = fast_calibrate;
 	return fast_calibrate;
-- 
1.8.2.1