linux-kernel - Re: Issue with commit a99790bf5c7f3d68d8b01e015d3212a98ee7bd57

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Message-Id: <3B9B63A0-E3CA-45EF-B291-5EC21F6F64F4@canonical.com>
Date:   Fri, 15 Feb 2019 00:44:33 +0800
From:   Kai Heng Feng <kai.heng.feng@...onical.com>
To:     Elias Rydberg <rydberg1995@...il.com>
Cc:     David Miller <davem@...emloft.net>,
        Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: Issue with commit a99790bf5c7f3d68d8b01e015d3212a98ee7bd57

Hi, 

> On Feb 15, 2019, at 12:17 AM, Elias Rydberg <rydberg1995@...il.com> wrote:
> 
> Dear Kai,
> 
> I write to you simply as I do not know exactly who to write, and since you are the author of commit a99790bf5c7f3d68d8b01e015d3212a98ee7bd57. If you are the completely wrong person to contact about this, I do apologize, and ask for you to share a resource guides me in the right direction. As of Dave, I CC you since you signed of the commit as well.
> 
> I will try to describe this with as few words as possible.
> 
> When upgrading to kernel 4.19 I experiened an issue of the screen starting to flicker, and then turn pitch black, whenever I turned on my wifi module. After som guidance, I found a workaround, namely booting with kernel parameter intel_idle.max_state=4. Not having a lot of experience with the Linux kernel, I thought it might have to do with an individual hardware fault in my machine.
> 
> This week I’ve been in contact with another person experiencing the exact same problems, and having the exact same laptop setup. I then investigated further, did my first kernel bisection, and found out that using a kernel with the named commit is causing this behaviour. This is the result from the bisection:
> 
> a99790bf5c7f3d68d8b01e015d3212a98ee7bd57 is the first bad commit
> commit a99790bf5c7f3d68d8b01e015d3212a98ee7bd57
> Author: Kai-Heng Feng <kai.heng.feng@...onical.com>
> Date:   Thu Jun 21 16:30:39 2018 +0800
> 
> 
> 
>     r8169: Reinstate ASPM Support
> 
> 
> 
>     On Intel platforms (Skylake and newer), ASPM support in r8169 is the
>     last missing puzzle to let CPU's Package C-State reaches PC8.  Without
>     ASPM support, the CPU cannot reach beyond PC3. PC8 can save additional
>     ~3W in comparison with PC3 on a Coffee Lake platform, Dell G3 3779.
> 
> 
> 
>     This is based on the work from Chunhao Lin <hau@...ltek.com>.
> 
> 
> 
>     Signed-off-by: Kai-Heng Feng <kai.heng.feng@...onical.com>
>     Signed-off-by: David S. Miller <davem@...emloft.net>
> 
> 
> 
> :040000 040000 87d4515c14f8eb8cf99b6f47f97ca4db700931c1 e542595c74609136a7094777afb10b83012f6643 M      drivers
> The spec on my latop is:
> CPU: Intel i7-8550U
> Wifi: Intel AC-9260 1730Mbps
> Memory: 8GB Kingston DDR4 2400MHz
> SSD: Samsung 970 EVO 500gb

>From platforms I’ve seen, if ASPM on r8169 is disabled, the deepest Package C-State on Intel CPU will limit to PC3.

If the ASPM on r8169 is enabled, it can reach to PC8 when the display is on, and be able to reach PC10 when display is off.

So the issue seems to be a platform bug - deeper Package C state makes your system unstable.

Please contact the system vendor, the deepest Package C state can be reach should be set by BIOS.

Kai-Heng

> 
> I’m not sure about the motherboard, but the model of the laptop case (and probably the motherboard) is Clevo N750WU.
> 
> Please ask if you need more information and I will provide as much help as I can.
> 
> Kind regards,
> Elias Rydberg