2025-05-04

My First Upstream Kernel Patch

Last week, I submitted my first patch to the Linux kernel, and it has already been queued in the for-leds-next branch. It’s satisfying to see my name appear in the commit history of software I work with every day — software that runs on an absurd number of devices. That said, I’m still a bit concerned and wondering how a syntax error like this slipped through the usual layers of review and tooling.

Commit: [PATCH] leds: pca995x: fix typo

I tried to compile the Linux Kernel Driver Database (LKDDb) and hit a parsing error:

error: builder for '/nix/store/a7r0c0ypz005r11y4cw8inz2ypvj32sd-lkddb-trunk.drv' failed with exit code 1
       last 20 log lines:
       > Running phase: unpackPhase
       > unpacking source archive /nix/store/ac9pm8xb0v18z0wn6fhjx9p67rl0s21w-source
       > source root is source
       > Running phase: buildPhase
       > KERNELVERSION is not set
       > with special includes.  Check them from time to time.
       > Traceback (most recent call last):
       >   File "/build/source/./build-lkddb.py", line 77, in <module>
       >     make(args, kerneldir, dirs)
       >   File "/build/source/./build-lkddb.py", line 25, in make
       >     tree.scan_sources()
       >   File "/build/source/lkddb/__init__.py", line 151, in scan_sources
       >     b.scan()
       >   File "/build/source/lkddb/linux/browse_sources.py", line 126, in scan
       >     s.in_scan(src, filename)
       >   File "/build/source/lkddb/linux/browse_sources.py", line 173, in in_scan
       >     parse_struct(scanner, scanner.struct_fields, line, dep, filename)
       >   File "/build/source/lkddb/linux/browse_sources.py", line 197, in parse_struct
       >     raise lkddb.ParserError("in parse_line(): %s, %s, %s" % (filename, line, param))
       > lkddb.ParserError: in parse_line(): drivers/leds/leds-pca995x.c, [' .compatible = "nxp,pca9955b"', ' . data = &pca9955b_chipdef '], . data = &pca9955b_chipdef
       For full logs, run:
         nix log /nix/store/a7r0c0ypz005r11y4cw8inz2ypvj32sd-lkddb-trunk.drv

The kernel turned out to have a simple typo that prevented the database from compiling.

Sending a patch

Contributing to the Linux kernel isn’t as daunting as it seems, once you understand the workflow. I referred to the official guide for contributing to the kernel throughout the process of figuring this out. Here’s how I sent my patch upstream, step by step.

Clone an up‑to‑date tree

git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
cd linux

Create a branch
```
git checkout -b leds-spacing-fix
```

Make the changes

In my case, I just removed the stray space between the ‘.’ and the ‘data’ field name:

diff --git a/drivers/leds/leds-pca995x.c b/drivers/leds/leds-pca995x.c
index 11c7bb69573e8c..6ad06ce2bf640a 100644
--- a/drivers/leds/leds-pca995x.c
+++ b/drivers/leds/leds-pca995x.c
@@ -197,7 +197,7 @@ MODULE_DEVICE_TABLE(i2c, pca995x_id);

 static const struct of_device_id pca995x_of_match[] = {
  { .compatible = "nxp,pca9952", .data = &pca9952_chipdef },
-	{ .compatible = "nxp,pca9955b", . data = &pca9955b_chipdef },
+	{ .compatible = "nxp,pca9955b", .data = &pca9955b_chipdef },
  { .compatible = "nxp,pca9956b", .data = &pca9956b_chipdef },
  {},
 };

Create a commit
```
git commit -s -m 'leds: pca995x: fix typo

Remove the stray space between the "." and the "data" field name in
the PCA995x device‑tree match table.

Signed-off-by: Jesse Karjalainen <[email protected]>'
```
The -s flag appends a Developer Certificate of Origin line to certify I wrote the patch. Ideally, you should also run style-check and test your changes. I skipped those because this one‑line fix is safe.
Generate a mail‑ready patch
```
git format-patch -1 --base=auto
```
This produces 0001-leds-pca995x-fix-spacing-typo.patch.

Find the maintainers

perl scripts/get_maintainer.pl 0001-*.patch

Which returned:

Lee Jones <lee@kernel.org> (maintainer:LED SUBSYSTEM)
Pavel Machek <pavel@kernel.org> (maintainer:LED SUBSYSTEM)
[email protected].org (open list:LED SUBSYSTEM)
[email protected].org (open list)

Configure email

I initially struggled with Outlook. Its mandatory OAuth authentication wouldn’t cooperate with git send-email, so I switched to my company account hosted on Hetzner instead, which worked like a charm.

Here is the NixOS Home Manager setup I ended up with:

accounts.email.accounts."ponkila" = {
  address = "[email protected]";
  userName = "[email protected]";
  realName = "Jesse Karjalainen";
  primary = true;
  imap = {
    host = "mail.your-server.de";
    port = 143;
    tls  = {
      enable = true;
      useStartTls = true;
    };
  };
  smtp = {
    host = "mail.your-server.de";
    port = 587;
    tls  = {
      enable = true;
      useStartTls = true;
    };
  };
  msmtp.enable = true;
};
programs.msmtp.enable = true;

programs.git = {
  userName  = "Jesse Karjalainen";
  userEmail = "[email protected]";
  extraConfig.sendemail = {
    smtpserver = "${pkgs.msmtp}/bin/msmtp";
  };
};

The guide at https://git-send-email.io/ was invaluable for testing the setup.

Send the patch

git send-email \
  --to "[email protected]" \
  --cc "Lee Jones <[email protected]>" \
  --cc "Pavel Machek <[email protected]>" \
  --cc "[email protected]" \
  0001-leds-pca995x-fix-spacing-typo.patch

Submitting my first kernel patch was a rewarding experience. It was a minor fix, but contributing to such a large and important project felt meaningful. And best of all — LKDDb builds cleanly now.