Fix suspend issues on Dell 7405 2-in-1

UPDATE SEPTEMBER 2021. S3 suspension was fixed on kernel 5.14 and this guide works again.

>UPDATE MARCH 2021. A patch to enable S0ix state on AMD Renoir hardware has been merged into kernel 5.11, but it does not work at all. In fact, this patch also broke the method to enable the S3 suspension described in this article. To get the latest updates about this issue follow the discussion on GitLab.

If you are a GNU/Linux user and bought this laptop (or any other laptop with Ryzen 4700U) recently , probably you found suspend to RAM does not work at all.

The root of all evil

Due to the new Windows "modern/connected standby" (S0ix) the good old sleep to RAM (S3) is disabled in some laptops. We need to patch our DSDT to make S3 available again.

AMD support for S0ix will be available soon, making this guide unnecessary (unless you want to save battery or have a decent and reliable sleep mode). Anyways, S0ix is garbage and people that designed it should have a place reserved in hell.

First of all, check S3 state and deep sleep mode are not available:

$ sudo dmesg | grep -i acpi | grep supports
[    0.357470] ACPI: (supports S0 S4 S5)

$ cat /sys/power/mem_sleep
[s2idle]

What's DSDT?

From the ArchLinux Wiki:

DSDT (Differentiated System Description Table) is a part of the ACPI specification. It supplies information about supported power events in a given system. ACPI tables are provided in firmware from the manufacturer. A common Linux problem is missing ACPI functionality, such as: fans not running, screens not turning off when the lid is closed, etc. This can stem from DSDTs made with Windows specifically in mind, which can be patched after installation. The goal of this article is to analyze and rebuild a faulty DSDT, so that the kernel can override the default one.

Basically a DSDT table is the code run on ACPI (Power Management) events.

Step 0: Use a recent Linux Kernel

Not directly related to the issue, but it's worth doing.

AMD Ryzen 4000 mobile processors require Linux Kernel v5.8 or above to perform correctly.

At the moment of writing this post, there are a few options to get this kernel: use openSUSE Tumbleweed, or installing a mainline kernel on Ubuntu. Also, it's supossed with the release of Ubuntu 20.04.2 (scheduled for October 2020) the kernel 5.8 will arrive to the Ubuntu HWE stack.

Step 1: Extract and decompile DSDT

Get acpidump and iasl, provided by the acpica package. Then, dump all your ACPI files into a directory:

$ mkdir acpi
$ cd acpi
$ sudo acpidump -b

And decompile the DSDT:

$ iasl -e *.dat -d dsdt.dat

This command produces a source file named dsdt.dsl.

Step 2: Recompile DSDT and examine errors

IMPORTANT: I updated the BIOS to v1.3.0 (Sep 18, 2020) immediately after purchasing this laptop. Errors and line numbers may vary depending on your BIOS version.

iasl -tc dsdt.dsl &> iasl_errors.txt

Look for errors in iasl_errors.txt with your text editor. For BIOS v1.3.0 you should have just three identical error messages pointing to lines 3965, 4002 and 4030.

Open dsdt.dsl, look for those lines and replace:

Return (Zero)

with:

Return (ToBuffer(Zero))

Then, re-run:

iasl -tc dsdt.dsl &> iasl_errors.txt

... and make sure there are no more errors on iasl_errors.txt.

Step 3: Enable S3 state

Search for this piece of code in dsdt.dsl:

    If ((CNSB == Zero))
    {
        If ((DAS3 == One))
        {
            Name (_S3, Package (0x04)  // _S3_: S3 System State
            {
                0x03, 
                0x03, 
                Zero, 
                Zero
            })
        }
    }

Then, remove the two if statements and fix the indentation accordingly:

Name (_S3, Package (0x04)  // _S3_: S3 System State
{
    0x03, 
    0x03, 
    Zero, 
    Zero
})

Step 4: Bump OEM version

Increase OEM version or otherwise the kernel will not apply the modified ACPI table. In line 21 replace:

line 21:    DefinitionBlock ("", "DSD   T", 1, "DELL  ", "WN09    ", 0x00000002)

with:

line 21:    DefinitionBlock ("", "DSD   T", 1, "DELL  ", "WN09    ", 0x00000003)

Step 5: Compile the final DSDT

iasl -ve -tc dsdt.dsl

Step 6: Create a cpio file

$ mkdir -p kernel/firmware/acpi
$ cp dsdt.aml kernel/firmware/acpi
$ find kernel | cpio -H newc --create > acpi_override
$ sudo cp acpi_override /boot

Step 7: Update GRUB

Edit file /etc/default/grub and append "mem_sleep_default=deep" to GRUB_CMDLINE_LINUX_DEFAULT parameter.

Then, add the line GRUB_EARLY_INITRD_LINUX_CUSTOM="acpi_override" below.

Finally, update GRUB with sudo update-grub (Debian/Ubuntu) or through YaST > System > Boot Loader in openSUSE (just make a minor change like increasing or decreasing timeout).

Step 8: Reboot

Reboot and check if S3 and deep sleep are enabled. You should see:

$ sudo dmesg | grep -i acpi | grep supports
[    0.502663] ACPI: (supports S0 S3 S4 S5)

$ cat /sys/power/mem_sleep
s2idle [deep]

Finally, try suspending to RAM.

References

• Fixing the DSDT of an Asus P8Z68V-Pro | Gentoo Forums
• Best practice to debug Linux* suspend/hibernate issues | 01.org
• Lenovo IdeaPad 5 14are05 - Suspend issues (S3 sleep fix) | ArchWiki
• Lenovo ThinkPad X1 Yoga (Gen 3) - Enabling S3 (before BIOS version 1.33) | ArchWiki
• AMD Ryzen 7 4700U suspend/hibernate not working on any kernel | Reddit
• Ideapad 14ARE05 S3 sleep fix | Reddit