Re: Kernel Freeze with American Megatrends BIOS

From: Roland Singer <roland.singer@desertbit.com>
To: Bjorn Helgaas <helgaas@kernel.org>
Cc: linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-acpi@vger.kernel.org, dri-devel@lists.freedesktop.org
Subject: Re: Kernel Freeze with American Megatrends BIOS
Date: Mon, 29 Aug 2016 20:46:17 +0200	[thread overview]
Message-ID: <1cca943f-eab4-4054-4a13-31370d7ae057@desertbit.com> (raw)
In-Reply-To: <20160829160210.GA24451@localhost>

Hi Bjorn,

I am using the bbswitch kernel module to switch off/on the GPU and
to obtain the GPU power state.
Obtaining the GPU state immediately after starting the graphical user
session freezes the system.

This code triggers something, which is responsible for the freeze.

---
// Returns 1 if the card is disabled, 0 if enabled
static int is_card_disabled(void) {
    u32 cfg_word;
    // read first config word which contains Vendor and Device ID. If all bits
    // are enabled, the device is assumed to be off
    pci_read_config_dword(dis_dev, 0, &cfg_word);
    // if one of the bits is not enabled (the card is enabled), the inverted
    // result will be non-zero and hence logical not will make it 0 ("false")
    return !~cfg_word;
}

static int bbswitch_proc_show(struct seq_file *seqfp, void *p) {
    // show the card state. Example output: 0000:01:00:00 ON
    dis_dev_get();
    seq_printf(seqfp, "%s %s\n", dev_name(&dis_dev->dev),
             is_card_disabled() ? "OFF" : "ON");
    dis_dev_put();
    return 0;
}
---

Either dis_dev_get or pci_read_config_dword is the trigger.

Link to the bbswitch module source code:
https://github.com/Bumblebee-Project/bbswitch/blob/master/bbswitch.c#L333

Am 29.08.2016 um 18:02 schrieb Bjorn Helgaas:
> [+cc linux-acpi, linux-kernel, dri-devel]
> 
> Hi Roland,
> 
> I have no idea how to debug this problem.  Are you seeing something
> that suggests it may be a PCI problem?
> 
> On Tue, Aug 23, 2016 at 11:23:45AM +0200, Roland Singer wrote:
>> Hi,
>>
>> hope somebody can help me fix this kernel problem which affects the following machines:
>>
>> - Clevo P651RA (i7-6700HQ/GTX 965M, part of the P6xxRx family which are also affected)
>> - MSI GE62 Apache Pro (i7-6700HQ/GTX 960M)
>> - Gigabyte P35V5 (i7-6700HQ/GTX 970M)
>> - Razer Blade 14" (2016) (i7-6700HQ/GTX 970M) (BIOS 5.11, 04/07/2016)
>>
>>
>> The kernel freezes if the graphical user session (Xorg & Wayland) is
>> started with a switched off discrete GPU card (NVIDIA).
>> If the discrete GPU is switched off after the graphical session start,
>> then everything works as expected, until the graphical session is restarted.
>>
>> This problem seams to be linked to specific BIOS settings. If the computer
>> is started with the following command line:
>>
>> acpi_osi=! acpi_osi="Windows 2009"
>>
>> then the kernel freeze does not occur anymore. However this required a special
>> ACPI DSDT firmware patch for the Razer Blade 2016 laptop:
>>
>> https://github.com/m4ng0squ4sh/razer_blade_14_2016_acpi_dsdt
>>
>> I strongly recommend to fix this in the kernel and I am ready to help and solve
>> this problem with some help.
>>
>> Here is a link to the GitHub issue with further information:
>>
>> https://github.com/Bumblebee-Project/Bumblebee/issues/764#issuecomment-241212595
>>
>> Here are some more detailed information:
>>
>> https://github.com/Lekensteyn/acpi-stuff/blob/master/Clevo-P651RA/notes.txt
>>
>> Hope somebody can help.