Re: [v3] x86/tsc: Unset TSC_KNOWN_FREQ and TSC_RELIABLE flags on Intel Bay Trail SoC

From: Hans de Goede <hdegoede@redhat.com>
To: vipul kumar <vipulk0511@gmail.com>, Thomas Gleixner <tglx@linutronix.de>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	Daniel Lezcano <daniel.lezcano@linaro.org>,
	linux-kernel@vger.kernel.org, Stable <stable@vger.kernel.org>,
	Srikanth Krishnakar <Srikanth_Krishnakar@mentor.com>,
	Cedric Hombourger <Cedric_Hombourger@mentor.com>,
	x86@kernel.org, Len Brown <len.brown@intel.com>,
	Vipul Kumar <vipul_kumar@mentor.com>
Subject: Re: [v3] x86/tsc: Unset TSC_KNOWN_FREQ and TSC_RELIABLE flags on Intel Bay Trail SoC
Date: Tue, 28 Jan 2020 15:23:29 +0100	[thread overview]
Message-ID: <329a2f7d-c5ed-6376-ec78-f00fa1ba41cd@redhat.com> (raw)
In-Reply-To: <CADdC98To8VKOUWnR+8zAJ04vgdc4vJoh2h96588+5XFer9YTJw@mail.gmail.com>

Hi,

On 28-01-2020 12:47, vipul kumar wrote:
> Hi Thomas,
> 
> Please find attached logs with mainline kernel version 5.4.15 with patch.

So the suggested change seems to not work, that is strange.

Can you double check you are running the correct kernel and
add the following change and gather debug output ? :

--- a/arch/x86/kernel/tsc_msr.c
+++ b/arch/x86/kernel/tsc_msr.c
@@ -102,6 +103,8 @@ unsigned long cpu_khz_from_msr(void)
         /* Get FSB FREQ ID */

+ pr_err("tsc msr id match %ld lo 0x%02x\n", id - tsc_msr_cpu_ids, lo);
+
         /* Map CPU reference clock freq ID(0-7) to CPU reference clock freq(KHz) */
         freq = freq_desc->freqs[lo & 0x7];

Regards,

Hans



> On Fri, Jan 24, 2020 at 9:24 PM Hans de Goede <hdegoede@redhat.com <mailto:hdegoede@redhat.com>> wrote:
> 
>     Hi,
> 
>     On 1/24/20 12:55 PM, Thomas Gleixner wrote:
>      > Hans,
>      >
>      > Hans de Goede <hdegoede@redhat.com <mailto:hdegoede@redhat.com>> writes:
>      >> On 1/24/20 9:35 AM, Thomas Gleixner wrote:
>      >>> Where does that number come from? Just math?
>      >>
>      >> Yes just math, but perhaps the Intel folks can see if they can find some
>      >> datasheet to back this up ?
>      >
>      > Can you observe the issue on one of the machines in your zoo as well?
> 
>     I haven't tried yet. Looking at the thread sofar the problem was noticed on
>     a system with a Celeron N2930, I don't have access to one of those, I
>     do have access to a system with a closely related N2840 I will give that
>     a try as well as see if I can reproduce this on one of the tablet
>     oriented Z3735x SoCs.
> 
>     I'll report back when I have had a chance to test this.
> 
>     Regards,
> 
>     Hans
> 

