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Re: [Qemu-devel] [PATCH] hw/display: Add basic ATI VGA emulation

From: BALATON Zoltan
Subject: Re: [Qemu-devel] [PATCH] hw/display: Add basic ATI VGA emulation
Date: Tue, 19 Feb 2019 16:11:15 +0100 (CET)
User-agent: Alpine 2.21.9999 (BSF 287 2018-06-16)

On Tue, 19 Feb 2019, Gerd Hoffmann wrote:
Which linux driver is this?

Those in linux/drivers/video/fbdev/aty/. This ati-vga model defaults to Rage
128 Pro (what PoweMac3,1 has, device id 0x5046) which is handled by the
aty128fb driver under Linux. MIPS fulong2e has Mobility Radeon M6 (RV100,
device id 0x5159) that you can also use as -device ati-vga,device_id=0x5159
which is driven by radeonfb under Linux.

So it could be tested with linux guests on x86 too I guess?
Can the radeon drm driver handle the devices too?

Yes you can try with x86 guests, I haven't tested that yet. The radeon driver only supports RV100 and up I think so may only work with the 0x5159 variant not with Rage 128 Pro which had another driver r128 but not sure that still exists. Although these two chips are similar, Rage 128 Pro is a bit simpler that's why I'm targeting it first and also that's what the PowerMac3,1 (the ppc mac99 machine is converging to) has. The R128Pro is the last of the previous generation before Radeon, while RV100 is the stripped down simplest version of the R100 family which has some more 3D capability). But even if the DRM driver loads, probably only the mode setting part is useful at the moment as 3D is not implemented yet by this device model. So not sure how useful that is at the moment. (It was tested that MacOS X can load the low level driver probably similar to Linux DRM:
but the high level rendering driver does not work yet. This was with v1 of this patch, I've made some fixes in v2 but likely that's not enough yet.)

I haven't thought about 3D yet as it's too early for that but for planning I know that the Xenia XBox 360 emulator (https://xenia.jp/) has some emulation of the Xenos chip https://en.wikipedia.org/wiki/Xenos_(graphics_chip) which is like the last of the Radeon family started with R100 so probably has way more features than needed for RV100 so we could emulate that similarly or even get up to later Radeons based on that in the future. We may look there for inspiration and maybe even code (altough have to convert from C++ and it only seems to care about the 3D part of the chip as the legacy stuff is missing from or not used in the XBox). So I've worked mostly on the legacy part and 2D for now and left 3D for later but unlikely that I'll be able to do that anytime soon so if someone is interested to take that up it would be very welcome. This should go into the yet missing ati_3d.c.

I'd also use model=<name> instead of device_id=... to switch between
different devices.

The only problem with that is that there are this many versions with confusing names (and maybe different device ids for different versions):


so the only really good way to identify a chip is via device_id. This is not user friendly but at this stage probably will do and we can add alternative model property later which aliases some device ids (like it's done for CPU selection). Just to avoid confusion between e.g. R128, R128P, RV100, Radeon7000, MobilityM6, R100 some of which refer to the same and some are different models.

(This table above is part of the X.org ATI page that has some useful info and also the Arch Linux https://wiki.archlinux.org/index.php/ATI page may have info about Linux drivers for these cards.)

You can add the driver to default_list[] in vl.c, then you don't need
-vga none to remove the default vga when adding -device ati-vga.

I could do that but since it's a bit unfinished (lacks advanced features
such as video overlay, 3D accel, command FIFO, etc.) and only a basic
implementation at the moment to work with Linux framebuffer that doesn't use
these features I thought it might be a godd idea to make it a bit harder to
access yet to avoid problem of someone trying it with a Windows guest with
drivers from ATI which probably will result in bad picture. But it's up to
you to decide if you want to add it to -vga option from the start or have it
as optional device and only add to -vga when it's more fully implemented and

It's not about "-vga ati".  This is about adding ati-vga to the list of
display devices, so qemu will not try to add a vga automatically in case
it finds "-device ati-vga" on the command line.  That way "qemu -device
ati-vga" will work fine, without "-vga none".

Adding -vga ati indeed only makes sense once the implementation is more

OK I thought those are related but if adding it to the default_list[] won't automatically add a -vga option then that's a good idea. I'll do that and also move the config lines to pci.mak in next version but wait for a few more days for more comments.


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