writing custom driver for VGA emulation ?

[Christian König]

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> on behalf of 
> Alex Deucher <alexdeucher at gmail.com>
> *Sent:* February 18, 2020 8:50 AM
> *To:* Yusuf Altıparmak <yusufalti1997 at gmail.com>
> *Cc:* amd-gfx list <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> 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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