Improve kernel portability and add ID EEPROM DT overlay support

[quorten]

Summary of changes:

• Add a shell script to assist in fetching the parport drivers for a specific older version of Linux, document in README. Useful for vintage fans if they have a preference toward a specific older version of Linux.

• Parameterize the version in the EEPROM, add README documentation for using an ID EEPROM to automatically load the drivers when the pi-parport board is attached.

• Update gpiod function contract fixes to conditionally check the version of Linux and use the corresponding function contract. I wasn't sure which Linux version made the change, so I just put in the latest version.

• Other small, helpful changes to READMEs throughout.

• Add Linux 5.4.0 build to Travis CI.

[quorten]

The driver changes were tested to successfully compile on two different versions of Raspbian. I haven't yet tested the driver changes recently made for the newer versions of Raspbian with actual hardware, but I'll probably get around to doing that soon.

[vonj]

Legacy parallel port scanners could work now on the Raspberry Pi with the original Windows drivers - there are versions of DOSBox and/or Qemu floating around with true parallel port support.

[quorten]

Cool, I should try running my Windows 98 QEMU virtual machine on a Raspberry Pi (via emulation) to test my scanner from Windows. It's probably going to be super slow on PiZero, unfortunately, but I could borrow my Pi4 for a test (currently being used for a different purpose).

[quorten]

I saw issue #38, so I also updated .travis.yml.

[vonj]

You may have better luck with https://dosbox-x.com/wiki/DOSBox%E2%80%90X’s-Feature-Highlights for running Windows 98

[quorten]

Yeah, sure thing, I've rebased and squashed my commits. Those extra commits for the EEPROM changes were just around from me fumbling around trying to figure out what would be the best way to implement the EEPROM changes!

[garlick]

Actually let's see how the travis builds do.

They seem to be running over here:

https://travis-ci.org/github/worlickwerx/pi-parport/builds/738151661

but I'll have to figure out why we don't see the links inline in the PR...

[garlick]

Ah so there are a few checkpatch errors in there that should be addressed. You should be able to run make check to do the check outside of travis.

Looks like maybe travis is slow today and some of the builders are taking a long time.

Weirdly, I could swear I saw the new kernel in the output earlier but it's not there now.

[quorten]

Cool, if Travis CI is working, I'll include the .travis.yml change to add a newer version of Ubuntu/Linux in my pull request to see how that goes.

[quorten]

Okay, so the current problem is that the Travis CI step for checkpatch.pl is still failing because of warnings on the inevitable LINUX_VERSION_CODE usage. we'd have to ignore that warning when reporting the exit status. The build on Linux 5.4.0 does work correctly, however.

In regard to the new kernel in the output: I did add a commit to update the Travis CI, then I removed it, now I added it back again.

[quorten]

The recent pushes ^ that rewrote all commits, just two changes really.

• Improve the script for fetching parport Linux source, git clone with --no-checkout.
• Move driver install out of README.md and into actual Makefiles.

[garlick]

This should suppress checkpatch warnings on LINUX_VERSION_CODE, if you'd like to tack this on.

diff --git a/driver/Makefile b/driver/Makefile
index 9501f15..ba1d753 100644
--- a/driver/Makefile
+++ b/driver/Makefile
@@ -16,7 +16,7 @@ modules clean:
        $(MAKE) -C $(KERNEL_PATH) M=$(shell pwd) $@

 check:
-       scripts/checkpatch.pl --no-tree -f parport_gpio.c
+       scripts/checkpatch.pl --ignore=LINUX_VERSION_CODE --no-tree -f parport_gpio.c

 install:
        mkdir -p $(MODDIR)/pi-parport

Perhaps let's change the PR title to something more descriptive like "improve kernel portability and ID EEPROM support"?

[quorten]

Alright, good to know we're okay with ignoring the LINUX_VERSION_CODE warnings, I've added the update to the Makefile. I've also changed the pull request title, so this should be all good to go.

[garlick]

Thanks! I'll hit the button once travis passes.

https://travis-ci.org/github/worlickwerx/pi-parport/builds/738348992

[garlick]

Travis is super slow today, and we've already gotten past the checkpatch test so I'll just go ahead and merge. Thanks again!

By the way, I would encourage you to update the wiki to document any attempts at reviving old gear, bootstrapping weird environments, or if you like, your board baking process. Pics would be neat. I know that sort of thing is time consuming though.

[quorten]

Those are really great ideas, I haven't yet assembled the second pi-parport board I've got but I'll be sure to take photos of the "before reflow" steps when I do! Then I can copy the other info I've put together when doing the first board and put up a nice wiki page for that.