[coreboot] Re: Sandybridge-M help request in setting up LVDS panel.

[Banik, Subrata]

HI Jose,

Some input inline.

Thanks,
Subrata

-----Original Message-----
From: Jose Trujillo [mailto:[e-mail]] 
Sent: Tuesday, December 3, 2019 7:44 PM
To: Banik, Subrata 
Cc: Nico Huber ; coreboot ; Patrick Georgi 
Subject: RE: [coreboot] Sandybridge-M help request in setting up LVDS panel.

Hello Friends
> > Hello All!
> > This is my first try in booting coreboot on a LVDS panel.
> > This is a Sandybridge-M system using video option ROM and VBT extracted from the original FW.
>
> if you ever want to get open-source gfx init running instead, let me know. It would only need a few more lines to force a specific mode with libgfxinit, maybe that is enough. And as you run the VBIOS ROM within coreboot, you are probably not interested in a resident VBIOS, are you?

[JT]->[Nico] I would prefer to do it with just libgfxinit but I don't have a remote idea in how to initialize the LVDS panel.
[JT]->[Nico] With a desktop monitor libgfxinit just work in this system but not a sign of activity on the panel.
[JT]->[Nico] I would like to know how to initialize the panel with just coreboot, so, please show me how.
[JT]->[Subrata] But also would like to know how to do it the right way with the blob.
> > VBE: Getting information about VESA mode 4116
>
> What mode is this 4116? Are you sure, you need this specific mode? Are you sure, your panel supports it? Sometimes, you need to specify a VBIOS (maybe even VBT) specific code to use the panel's native resolution.
>
> [Subrata] VBE: resolution for 4116: 1024x768@16. Its depends on your panel support and VBIOS support.

[JT] I just set at menuconfig 1024x768 1-5-5-5 and I have not idea why is reporting 4116-16 bit the intended is 18 bit.
[JT]->[Subrata] Do I need to configure something else or create some code for this?

[Subrata] By default I could see CB was picking 0x118 which was causing issue for me.
Later based on die msg, I have set below config to make it work on my platform + DGPU

#
# Display
#
CONFIG_FRAMEBUFFER_SET_VESA_MODE=y
CONFIG_FRAMEBUFFER_VESA_MODE_116=y
CONFIG_FRAMEBUFFER_VESA_MODE=0x116
> > VBE: Function call failed!
> > Error: In vbe_get_mode_info function
>
> I don't think coreboot should halt here. Problems with the graphics are non-fatal.
>
> [Subrata] Please have a look at https://review.coreboot.org/c/coreboot/+/34284. What I found was sometime Coreboot tries to fixed a mode which might not be supported by that VBIOS hence we might see issue during payload and further because it would try to map display to 0 resolution if mode set is not correct. Hence I had listed the supported VESA mode in debug print. If you could try to use supported one, it might work.

[JT] Halts with a "die" function because anyway if is not halted it will be halted by Tianocore with division by zero.
[JT]->[Subrata] The LVDS panel supports 1024x768 18 and 24 bit but the LVDS cable only can transfer 18 bits.
[JT]->[Subrata] The original FW support those LVDS resolutions too and I suppose VBIOS too.
[JT]->[Subrata] At 1024x768 1-5-5-5 is the only setting that shows signs of panel initialization and shows output on the panel but halts.
[JT] The other 2 1024x768 variants shows vertical stripes on the panel and gets halted anyway.
[JT] This system doesn't dump the list of supported VESA modes even if I comment the "die" function.

Thank you,
Jose Trujillo.