linux-kernel - [PATCH] x86/intel: Add comments about why we disabled HPET on Baytrail

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Date:	Mon, 15 Jun 2015 17:40:01 +0800
From:	Feng Tang <feng.tang@...el.com>
To:	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
	len.brown@...el.com, john.stultz@...aro.org
Cc:	matthew.lee@...el.com, Feng Tang <feng.tang@...el.com>
Subject: [PATCH] x86/intel: Add comments about why we disabled HPET on Baytrail

The question has been asked many times, and finally I found the
official document which explains the problem of HPET on Baytrail
that it will halt in deep idle states.

Signed-off-by: Feng Tang <feng.tang@...el.com>
---
 arch/x86/kernel/early-quirks.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/early-quirks.c b/arch/x86/kernel/early-quirks.c
index fe9f0b7..9cdc6acb 100644
--- a/arch/x86/kernel/early-quirks.c
+++ b/arch/x86/kernel/early-quirks.c
@@ -628,7 +628,10 @@ static struct chipset early_qrk[] __initdata = {
 	  QFLAG_APPLY_ONCE, intel_graphics_stolen },
 	/*
 	 * HPET on current version of Baytrail platform has accuracy
-	 * problems, disable it for now:
+	 * problems, that it will halt in deep idle state, so disable it.
+	 *
+	 * Please refer section 18.10.1.3 of http://www.intel.com/content/dam/www/public/us/en/documents/datasheets/atom-z8000-datasheet-vol-1.pdf 
+	 * for more details.
 	 */
 	{ PCI_VENDOR_ID_INTEL, 0x0f00,
 		PCI_CLASS_BRIDGE_HOST, PCI_ANY_ID, 0, force_disable_hpet},
-- 
1.7.9.5

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