Re: writing custom driver for VGA emulation ?

[Christian König <christian.koenig@xxxxxxx>]

Yusef is using an ARM platform. As far as I know he already tried to shuffle the static allocation for the MMIO address spaces around without much luck.

The only option I see would be to use the PCIe bridge trick I've mentioned below, but this is really so hacky that I won't recommend that.

Christian.

Am 18.02.20 um 15:43 schrieb Bridgman, John:

[AMD Official Use Only - Internal Distribution Only]

>And we already checked, 256MB is unfortunately the minimum you can resize the VRAM BAR on the E9171 to.

Ahh, OK... I didn't realize we had already looked into that. I guess that approach isn't going to work.

Yusef, guessing you are using a 32-bit CPU ? Is it possible to talk to whoever does SBIOS for your platform to see if you could maybe reduce address space allocated to RAM and bump up the MMIO space ?

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From: Christian König <ckoenig.leichtzumerken@xxxxxxxxx>
Sent: February 18, 2020 9:19 AM
To: Bridgman, John <John.Bridgman@xxxxxxx>; Alex Deucher <alexdeucher@xxxxxxxxx>; Yusuf Altıparmak <yusufalti1997@xxxxxxxxx>
Cc: amd-gfx list <amd-gfx@xxxxxxxxxxxxxxxxxxxxx>
Subject: Re: writing custom driver for VGA emulation ?

 

The problem Yusuf runs into is that his platform has multiple PCIe root hubs, but only 512MB of MMIO address space. That is not enough to fit all the BARs of an E9171 into.

But without the BARs neither the VGA emulation nor amdgpu not anything else will work correctly.

And we already checked, 256MB is unfortunately the minimum you can resize the VRAM BAR on the E9171 to.

What could maybe work is to trick the upstream bridge of the VGA device into not routing all the addresses to the BARs and actually use only a smaller portion of visible VRAM. But that would be highly experimental and requires a rather big hack into the PCI(e) subsystem in the Linux kernel.

Regards,
Christian.

Am 18.02.20 um 15:08 schrieb Bridgman, John:

[AMD Official Use Only - Internal Distribution Only]

Does the VBIOS come up with something like a splash screen, ie is VBIOS able to initialize and drive the card ?

If so then another option might be to use a VESA driver rather than VGA.

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From: amd-gfx <amd-gfx-bounces@xxxxxxxxxxxxxxxxxxxxx> on behalf of Alex Deucher <alexdeucher@xxxxxxxxx>
Sent: February 18, 2020 8:50 AM
To: Yusuf Altıparmak <yusufalti1997@xxxxxxxxx>
Cc: amd-gfx list <amd-gfx@xxxxxxxxxxxxxxxxxxxxx>
Subject: Re: writing custom driver for VGA emulation ?

 

On Tue, Feb 18, 2020 at 2:56 AM Yusuf Altıparmak
<yusufalti1997@xxxxxxxxx> wrote:
>
> Hello AMD team;
>
> I have E 9171 GPU and want to use it on a embedded system which has limited MMIO space on PCIe bus (MAX 512 MB).
>
> I received feedbacks that I can only use VGA emulation with this memory space. I was unable to get 'amdgpu' driver working with Xorg due to I had many errors(firmwares are not loading) in each step and tired of solving them one by one.
>
> I want to write a simple custom driver for this GPU with kernel version 4.19.
> Is it possible to print some colors on screen with a custom driver over PCIe communication ? or writing some words on screen as VGA ?
>
> If answer is yes, then which code pieces (on amdgpu driver folder) or reference documentation should I use? I have Register Reference Guide.pdf.
>
> I will be appreciated for your guidance.

That is not going to do what you want on your platform.  The VGA
emulation requires that you set up the card first to enable it, which
in turn requires MMIO access and thus you are back to square one.

Alex
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