Re: [PATCH] vga-switcheroo: Allow VGA_SWITCHEROO to be enabled on LoongArch

[Thomas Zimmermann]

Hi

Am 30.10.26 um 09:39 schrieb zhaotianrui:
> 在 2026/10/30 下午4:17, Thomas Zimmermann 写道:
> > Hi
> >
> > Am 30.10.26 um 08:04 schrieb zhaotianrui:
> > > 在 2026/10/29 下午4:16, Thomas Zimmermann 写道:
> > > > Hi
> > > >
> > > > Am 29.10.26 um 02:36 schrieb Tianrui Zhao:
> > > > > LoongArch systems with hybrid graphics (integrated +
> > > > > discrete GPU) can benefit from the same GPU switching
> > > > > mechanism that x86 laptops use. Relax the dependency
> > > > > to allow VGA_SWITCHEROO to be built on LoongArch,
> > > > > consistent with the existing dependencies on ACPI,
> > > > > PCI, and FB=y.
> > > > >
> > > > > Change-Id: I84d38fdfe5e1591495fb3681474a7f1f64281fa8
> > > >
> > > > Internal change ids should be remove before submitting patches.
> > > Thanks for your review, I will fix this.
> > >
> > >
> > > Best regards
> > >
> > > Tianrui Zhao
> > >
> > > > > Signed-off-by: Tianrui Zhao <zhaotianrui@xxxxxxxxxxx>
> > > > > ---
> > > > >   drivers/gpu/vga/Kconfig | 2 +-
> > > > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > > > >
> > > > > diff --git a/drivers/gpu/vga/Kconfig b/drivers/gpu/vga/Kconfig
> > > > > index bad4bcee313..89edd1211aa 100644
> > > > > --- a/drivers/gpu/vga/Kconfig
> > > > > +++ b/drivers/gpu/vga/Kconfig
> > > > > @@ -1,7 +1,7 @@
> > > > >   # SPDX-License-Identifier: GPL-2.0-only
> > > > >   config VGA_SWITCHEROO
> > > > >       bool "Laptop Hybrid Graphics - GPU switching support"
> > > > > -    depends on X86
> > > > > +    depends on X86 || LOONGARCH
> > > >
> > > > I'm a bit skeptical if that's all there is to do.  Does loongarch 
> > > > really work with the existing handlers in the graphics drivers 
> > > > as-is?  See [1] for the interface that implements the actual 
> > > > switching.
> > > >
> > > > [1] 
> > > > https://elixir.bootlin.com/linux/v7.3/source/include/linux/vga_switcheroo.h#L93
> > > >
> > > > Best regards
> > > > Thomas
> > > Thanks,  I will carefully check whether all these 
> > > vga_switcheroo_handler callbacks are supported on the LoongArch 
> > > platform.
> >
> > Switcheroo used to be required for x86 notebooks from ~2010. Those 
> > systems had two graphics cards, but only one set of output 
> > connectors. That design is become rare, I think.
> >
> > So I'm a bit surprised to see it come back. Which loongarch systems 
> > are there?
> >
> > Best regards
> > Thomas
> Hi Thomas,
>
> Thanks for your reply.
>
> On the Loongson platform, we don't have the "two GPUs but only one set 
> of display outputs" scenario you described. However, we do have 
> systems where an integrated GPU and a discrete GPU coexist.
> We would like to use the vga_switcheroo interface to switch between 
> the discrete GPU (DIS) and the integrated GPU (IGD), and to configure 
> the default VGA device.
> Would this approach be feasible? Do you have any suggestions or 
> recommendations?

Oh, that's not what vga_switcheroo is for. For your scenario, simply 
provide a DRM driver for each GPU. Selection of the boot-up display 
happens in the UEFI/BIOS.  Picking the correct display hardware at 
runtime is left to clients in user space (or fbcon). DRM itself has not 
preference.

Best regards
Thomas

> Best regards
> Tianrui Zhao
> > > Best regards
> > >
> > > Tianrui Zhao
> > >
> > > > >       depends on ACPI
> > > > >       depends on PCI
> > > > >       depends on FB=y

--
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com
GF: Stefan Gaiser, Jochen Jaser, Abhinav Puri, (HRB 36809, AG Nürnberg)