Fix serial backlight fix breaking

[cflee]

#3586 seems to be breaking rgblight for I2C split boards, see r/olkb comment thread and thread2

This PR reverts it and offers a substitute fix: tweak keyboard_slave_loop() to always run backlight_set() on every loop, ignoring the BACKLIT_DIRTY flag, which is effectively what #3586 has done except in the slave matrix scan instead.

Technically it only needs to run every time there's a serial transaction from master since that will always update the backlight byte, so we could change the serial code to update the BACKLIT_DIRTY flag. But it seems like the intent in the rgblight section in keyboard_slave_loop() is that serial mode doesn't use the flags, so I think this makes sense. I also don't want to mess with the serial code...

Note: I don't have a serial split board to test this with, but my lets_split_eh which uses I2C works with this.

[SethBarberee]

I’ll get to testing it later today/tomorrow

[drashna]

@nooges and @That-Canadian This look okay to you? And if you have time, does it work fine?

[SethBarberee]

From my testing on my EE_HANDS Serial Iris, everything works fine. Nice work!

[Lenbok]

@drashna Is it OK to merge this fix? I don't want to update qmk on my board while the current master has the bug that this fixes.

[drashna]

Hmm, it looks like this may have some conflicts with #3886

[cflee]

@drashna I will look at that PR more closely again, but it seems like the first and third commit roughly achieve what this PR does (but by setting BACKLIT_DIRTY instead of the split_util.c change here to isolate that flag to I2C only), so the remaining diff in the second commit is:

diff --git a/quantum/split_common/matrix.c b/quantum/split_common/matrix.c
index 6a9ce66d27..457db143dd 100644
--- a/quantum/split_common/matrix.c
+++ b/quantum/split_common/matrix.c
@@ -237,7 +237,7 @@ int i2c_transaction(void) {
             if (err) goto i2c_error;
             
             // Write backlight 
-            i2c_master_write(get_backlight_level());
+            i2c_master_write( backlight_config.enable ? backlight_config.level : 0 );
             
             BACKLIT_DIRTY = false;
         }

[evantravers]

Where does this stand? Is there anything I can do to help?

[evantravers]

@cflee I can try and test this… what are the testing steps?

[cflee]

@evantravers I guess you also have a Let's Split Eh? If your branch is ahead of this or up to date with master, you could either manually apply the changes as displayed in the Files changed tab, or cherry pick the two commits from this PR into your branch.

Without this fix on latest master, rgblight changes shouldn't be working on the slave side; with this fix rgblight should work fine.

[evantravers]

@cflee I'm going to assume that I need to flash that firmware onto both halves, right?

[evantravers]

It works for me on my let's split eh.

Turns out you only need to flash that change on the slave… but I flashed on both to be sure.

[paulbdavis]

Also working on my let's split eh?

My user setup is on top of the current master, with these two commits applied on top and everything is working fine, but I do not have a setup to test for regressions to non-RGB backlighting (maybe just a different config setup can test that on my hardware?).