No backlight control when resuming from suspend-to-ram

Similar problems here.  It will also spontaneously reboot after resume from time to time.

I believe that the BIOS is corrupting itself on resume.  You can check this by running dmidecode as root before the first suspend, then after resume.  You will note that it works perfectly before a resume, but that the tables are corrupted after resume.

Yes, I noticed that and saw your other thread on this issue as well.  I just received my laptop so it came with a newer BIOS revision than the 1.2 version that you previously mentioned, does suspend and resume work properly for you with the older firmware?  Since I effectively can't get the USB-C port to do anything (save for charge my Nexus 6P), I guess the Thunderbolt improvements in the newer BIOS revisions are largely moot from a user standpoint.  

Suspend and resume is more stable with the older BIOS, though it still corrupts itself and will spontaneously reboot on resume.  That said, I very, very rarely (never?) saw a resume that left me with a blank screen, and that is very common with 1.2.10.

Neither is fully stable.  

I see same problem with brightness after resume not working.

In /sys/class/backlight/intel_backlight I can still turn on off display with the bl_power or by setting brightness to 0. All other values (up to 12 supported) just gives full brightness. This i with bios 1.2.10 on Linux 4.7.2-1-ARCH on Arch Linux.

My Dell Precision 5510 is an intel i5-6440HQ without discrete graphic (No Nvidia).

In a bug reported 2013-07-26 I found a reference to a temporary workaround:
https://bugzilla.kernel.org/show_bug.cgi?id=60635
https://bugs.freedesktop.org/show_bug.cgi?id=97486

On my PC: after fresh poweron:

$ sudo intel_reg read 0xc2000

(0x000c2000): 0x00000001

After suspend/resume where brightness is not working the value of the register had changed to 0's. Running the following solved the problem an it is possible to adjust the brightness:

$ sudo intel_reg write  0xc2000 0x00000001

A patch for the kernel is discussed here: https://patchwork.freedesktop.org/patch/109407/

But as it is not yet finalized it could take until kernel 4.9 before we see it in the Linux kernel.

So I actually only ran into this problem once, I usually am unable to resume from sleep because of other issues mentioned on this board. But one peculiarity I did see when I hit it was I was able to adjust brightness by some means but not others. So my normal means is:

"xbacklight -inc 10" and "xbacklight -dec 10"

But those weren't working. But when I did this via xrandr, that did work. Something like:

"xrandr --output eDP1 --brightness 0.7

Of course I can't recreate because I usually have to reboot :(. Though I saw this on Dell Precision 5510 with nvidia quadro 1000m and bios 1.2.14.

Thanks for finding and sharing that patch.  I can confirm that the patch seems to fix my suspend and resume issues with respect to the backlight.  I'm able to consistently resume and still have my screen on and can control my backlight.

Indeed - this was the issue with my Dell Precision 5510 currently running Ubuntu 16.04.1 (But was present on the as-delivered 14.04). My BIOS is currently: "DMI: Dell Inc. Precision 5510/08R8KJ, BIOS 1.2.14 08/31/2016". I'm currently on kernel 4.6.0-040600-generic.

Unfortunately Suspend does not complete if I'm connected to the WD15 docking station but this is at least some progress - Honestly it is frustrating that these issues exist on a box that is being sold pre-installed with Ubuntu OS.

Following MortenS's reply I wrote a script for:

/usr/lib/pm-utils/sleep.d/97fixbacklight - (Don't forget to chmod 755)

======================8<======================
#!/bin/sh
# From patchwork.freedesktop.org/.../
# and en.community.dell.com/.../19985320
# Suspend Resume fails to restore PWM_GRANUALITY
# Tony.Jewell@Cregganna.Com

#. "${PM_FUNCTIONS}"

INTEL_REG=/usr/bin/intel_reg
ADDR="0x000c2000"
SAVE_FILE=/var/lib/pm-utils/save_intel_reg_pwm_granuality

[ -x "$INTEL_REG" ] || exit 0

case "$1" in
        hibernate|suspend)
		echo "$0: Saving Intel Register PWM_GRANUALITY"
		"$INTEL_REG" read "$ADDR" \
			| (read addr value && echo "$value") \
			>"$SAVE_FILE"
	sync
	;;
	thaw|resume)
		value=`cat "$SAVE_FILE" 2>/dev/null`
		if [ -n "$value" ]
		then
			echo "$0: Restoring Intel Register PWM_GRANUALITY $value"
			"$INTEL_REG" write "$ADDR" "$value"
			rm "$SAVE_FILE"
		fi
	;;
esac
======================8<======================

Thanks HSAHMED - on my system I think that would go in:

/lib/systemd/system-sleep/fixbacklight

not in

/usr/lib/systemd/system-sleep/fixbacklight 

@hsahmed and @creggann I wanted to let you know that the systemd fixbacklight script, saved to /lib/systemd/system-sleep/fixbacklight has worked perfectly for me. I have been fighting this issue since the beginning of August. I have spent a couple weekends, 2 reinstalls, and several additional evenings trying things.

My system is the Dell M5510 running Ubuntu 16.04. 

Same here.  My resume now works perfectly.  Thanks!

It works also for my Dell Precision 5510. Thanks!

Thanks for sharing this script. I tried it on my Precision workstation 5510 after updating the bios to 1.2.14 (A13). Seems like it didn't do the trick on that machine. Running Arch Linux with Kernel 4.7.6.

My apologies, the script works fine. It was my mistake that I didn't check to see if the intel_reg tool which is required was present at /usr/bin/intel_reg I installed the intel-gpu-tools package and all is well. Sorry about the previous inaccurate post.

On Fedora 24, intel_reg command does not exist. Intsead there are commands intel_reg_read and intel_reg_write.

Here is a modified script that works on Fedora 24:

#!/bin/sh
# From patchwork.freedesktop.org/.../
# and en.community.dell.com/.../19985320
# Suspend Resume fails to restore PWM_GRANUALITY
# Based on script by Tony.Jewell@Cregganna.Com

INTEL_REG_READ=/usr/bin/intel_reg_read
INTEL_REG_WRITE=/usr/bin/intel_reg_write

ADDR="0x000c2000"
SAVE_FILE=/var/lib/systemd/save_intel_reg_pwm_granuality

[ -x "$INTEL_REG_READ" ] || exit 1
[ -x "$INTEL_REG_WRITE" ] || exit 1

case "$1" in
        pre)
		"$INTEL_REG_READ" "$ADDR" \
			| (read addr colon value && echo "$value") \
			>"$SAVE_FILE"
		echo "$0: Saving Intel Register PWM_GRANUALITY \"$value\""
	sync
	;;
	post)
		value=`cat "$SAVE_FILE" 2>/dev/null`
		if [ -n "$value" ]
		then
			echo "$0: Restoring Intel Register PWM_GRANUALITY \"$value\""
			"$INTEL_REG_WRITE" "$ADDR" "$value"
			rm "$SAVE_FILE"
		fi
	;;
esac