framebuffer: red and blue are swapped on devices using MSM8974

I noticed that when using the framebuffer display with wayland on weston or plasma-mobile, the red and blue colors are swapped.
The problem has been found in the following devices, all sharing the MSM8974 SoC:

• oneplus-bacon, reported by @Nimayer
• samsung-klte, reported by @minlexx
• fairphone-fp2, reported by @z3ntu

Edit: The problem has been solved

Apparently the problem was due to an inverted byte order of the pixel format in the framebuffer driver.

Problem has been fixed with:

• !287 (merged) for oneplus-bacon
• !291 (merged) for samsung-klte
• !292 (merged) for fairphone-fp2

Here is an example picture of the problem

Also saw this on fairphone-fp2 (also msm8974 - but the AC doesn't matter apparently^^)

By Luca Weiss on 2019-03-15T10:37:21

mentioned in merge request !263 (closed)

By Federico Amedeo Izzo on 2019-03-15T11:02:03

mentioned in issue #204 (closed)

By Federico Amedeo Izzo on 2019-03-15T11:11:14

Thank you @z3ntu, updated the description.

By Federico Amedeo Izzo on 2019-03-15T11:14:51

changed title from framebuffer: red and blue are swapped on devices using MSM8974AC to framebuffer: red and blue are swapped on devices using MSM8974

By Federico Amedeo Izzo on 2019-03-15T11:13:09

changed the description

By Federico Amedeo Izzo on 2019-03-15T11:13:09

changed the description

By Federico Amedeo Izzo on 2019-03-15T11:14:21

added category::device help wanted type::bug labels

Thanks for opening the issue!

Here are some color problems related troubleshooting tips that affected users could try out: https://wiki.postmarketos.org/wiki/Troubleshooting:display#My_screen_is_red.21

By Oliver Smith on 2019-03-15T17:55:54

mentioned in commit wiki@a9db28e2

By postmarketOS Wiki bot on 2019-03-15T18:42:50

I figured out the framebuffer color problem and managed to solve it on oneplus-bacon,
and I think the same fix can be applied also to samsung-klte and fairphone-fp2, with a small change.

I will open soon a MR for oneplus-bacon which I tested myself and for other two phones which will need testing.

TL:DR: the bytes of the framebuffer pixel format are in reverse order

Problem explaination

According to MSM8974 framebuffer driver the byte order of the pixel format is the following:

RGBA: | A | B | G | R |
ARGB: | B | G | R | A |

Where R,G,B are red, green and blue channels and A is alpha (transparency)

Assuming that instead the oneplus-bacon framebuffer format is RGBA but in reverse order

hardware RGBA: | R | G | B | A |
k. driver RGBA: | A | B | G | R |

We can see that the stock kernel driver provides images where A corresponds to R on hardware (possible source of red screen problem)

The original fix i pushed for oneplus-bacon red screen problem was the first one suggested on display troubleshooting,
which is using the format RGB instead of RGBA.
Which works but with swapped B and G.

hardware RGBA: | R | G | B | A |
k. driver RGB: | B | G | R | |

The RGB solution probably displays correct image because there is padding corresponding to the hardware alpha channel,
but as we can see R and B are swapped in driver w.r.t hardware.

Solution

Apply a patch equivalent to the alternative patch proposed in display troubleshooting which inverts the order of bytes in the framebuffer driver.

Once the order is inverted, oneplus-bacon works fine with RGBA color setting,
while samsung-klte and fairphone-fp2 that did not have the red screen problem,
probably need the patch and ARGB color setting.

samsung-klte example:

hardware ARGB: | A | R | G | B |
k. driver RGBA: | A | B | G | R | |

Which explains why stock kernel results in R and B being swapped.

Merge requests

As I said, I will open MR for oneplus-bacon, samsung-klte and fairphone-fp2

By Federico Amedeo Izzo on 2019-03-23T11:16:50

mentioned in merge request !287 (merged)

By Federico Amedeo Izzo on 2019-03-23T12:58:20

@ollieparanoid thank you for the suggestion that drove me in the right direction.

This issue is solved for oneplus-bacon in !287 (merged),
I will open MR for other two phones soon.

By Federico Amedeo Izzo on 2019-03-23T13:00:57

mentioned in commit wiki@69b589e2

By postmarketOS Wiki bot on 2019-03-25T08:43:38

I will be happy to test your PR on samsung-klte. Or I'll test fix myself today or tomorrow...

By Alexey Min on 2019-03-25T21:34:34

I opened MR !291 (merged) with fix for samsung-klte, @minlexx can you test it?
I will remove the WIP: once you tell me it's working :)

By Federico Amedeo Izzo on 2019-03-25T21:34:42

mentioned in merge request !291 (merged)

By Federico Amedeo Izzo on 2019-03-25T21:31:43

mentioned in commit 85904de7

By Luca Weiss on 2019-03-27T17:24:21

mentioned in merge request !292 (merged)

By Luca Weiss on 2019-03-27T17:25:38

Opened !292 (merged) for the Fairphone 2. Thanks for the patch @Nimayer !

By Luca Weiss on 2019-03-27T17:26:55

mentioned in commit 3eae1451

By Luca Weiss on 2019-03-28T15:05:36

mentioned in commit 874a309e

By Luca Weiss on 2019-03-28T15:06:55

changed the description

By Federico Amedeo Izzo on 2019-03-30T09:44:53

Updated the description mentioning related MR.

I'm closing this issue since the problem is solved

By Federico Amedeo Izzo on 2019-03-30T09:45:32

closed

By Federico Amedeo Izzo on 2019-03-30T09:45:33