writing custom driver for VGA emulation ?

Tue Feb 18 14:57:28 UTC 2020

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 ?
>
> ------------------------------------------------------------------------
> *From:* Christian König <ckoenig.leichtzumerken at gmail.com>
> *Sent:* February 18, 2020 9:19 AM
> *To:* Bridgman, John <John.Bridgman at amd.com>; Alex Deucher 
> <alexdeucher at gmail.com>; Yusuf Altıparmak <yusufalti1997 at gmail.com>
> *Cc:* amd-gfx list <amd-gfx at lists.freedesktop.org>
> *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.
>>
>>
>> ------------------------------------------------------------------------
>> *From:* amd-gfx <amd-gfx-bounces at lists.freedesktop.org> 
>> <mailto:amd-gfx-bounces at lists.freedesktop.org> on behalf of Alex 
>> Deucher <alexdeucher at gmail.com> <mailto:alexdeucher at gmail.com>
>> *Sent:* February 18, 2020 8:50 AM
>> *To:* Yusuf Altıparmak <yusufalti1997 at gmail.com> 
>> <mailto:yusufalti1997 at gmail.com>
>> *Cc:* amd-gfx list <amd-gfx at lists.freedesktop.org> 
>> <mailto:amd-gfx at lists.freedesktop.org>
>> *Subject:* Re: writing custom driver for VGA emulation ?
>> On Tue, Feb 18, 2020 at 2:56 AM Yusuf Altıparmak
>> <yusufalti1997 at gmail.com> <mailto:yusufalti1997 at gmail.com> 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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