add blog post about change kernel params with ansible

jekyll/_posts/ansible-edit-kernel-params/2023-06-19-ansible-edit-grub.md

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+---
+layout: post
+title:  Using Ansible to alter Kernel Parameters
+date:   2023-06-19 09:31:00 Europe/Amsterdam
+categories: ansible grub linux
+---
+
+For months, I've had a peculiar problem with my laptop: once in a while, seemingly without reason, my laptop screen would freeze.
+This only happened on my laptop screen, and not on an external monitor.
+I had kind of learned to live with it as I couldn't find a solution online.
+The only remedy I had was reloading my window manager, which would often unfreeze the screen.
+
+Yesterday I tried Googling once more and I actually found [a thread](https://bbs.archlinux.org/viewtopic.php?id=246841) about it on the Arch Linux forums!
+They talk about the same laptop model, the Lenovo ThinkPad x260, having the problem.
+Fortunately, they also propose [a temporary fix](https://bbs.archlinux.org/viewtopic.php?pid=1888932#p1888932).
+
+# Trying the Fix
+
+Apparently, a problem with the Panel Self Refresh (PSR) feature of Intel iGPUs is the culprit.
+According to the [Linux source code](https://github.com/torvalds/linux/blob/45a3e24f65e90a047bef86f927ebdc4c710edaa1/drivers/gpu/drm/i915/display/intel_psr.c#L42), PSR enables the display to go into a lower standby mode when the sytem is idle but the screen is in use.
+These lower standby modes can reduce power usage of your device when idling.
+
+This all seems useful, except when it makes your screen freeze!
+The proposed fix disables the PSR feature entirely.
+To do this, we need to change a parameter to the Intel Graphics Linux Kernel Module (LKM).
+The LKM for Intel Graphics is called `i915`.
+There are [multiple ways](https://wiki.archlinux.org/title/Kernel_parameters) to change kernel parameters, but I chose to edit my Grub configuration.
+
+First, I wanted to test whether it actually works.
+When booting into my Linux partition via Grub, you can press `e` to edit the Grub definition.
+Somewhere there, you can find the `linux` command which specifies to boot Linux and how to do that.
+I simply appended the option `i915.enable_psr=0` to this line.
+After rebooting, I noticed my screen no longer freezes!
+Success!
+
+# Persisting the Fix
+
+To make the change permanent, we need to permanently change Grub's configuration.
+One way to do this, is by changing Grub's defaults in `/etc/default/grub`.
+Namely, the `GRUB_CMDLINE_LINUX_DEFAULT` option specifies what options Grub should pass to the Linux kernel by default.
+For me, this is a nice solution as the problem exists for both Linux OSes I have installed.
+I changed this option to:
+```ini
+GRUB_CMDLINE_LINUX_DEFAULT="quiet splash i915.enable_psr=0"
+```
+
+Next, I wanted to automate this solution using Ansible.
+This turned out to be quite easy, as the Grub configuration looks a bit like an ini file (maybe it is?):
+```yaml
+- name: Edit grub to disable Panel Self Refresh
+  become: true
+  ini_file:
+    path: /etc/default/grub
+    section: null
+    option: "GRUB_CMDLINE_LINUX_DEFAULT"
+    value: '"quiet splash i915.enable_psr=0"'
+    no_extra_spaces: true
+  notify: update grub
+```
+
+Lastly, I created the `notify` hook to update the Grub configuration:
+```yaml
+- name: update grub
+  become: true
+  command:
+    cmd: update-grub
+```
+
+# Conclusion
+
+It turned out to be quite easy to change Linux kernel parameters using Ansible.
+Maybe some kernel gurus have better ways to change parameters, but this works for me for now.
+
+As a sidenote, I started reading a bit more about NixOS and realised that it can solve issues like these much more nicely than Ansible does.
+I might replace my OS with NixOS some day, if I manage to rewrite my Ansible for it.