Re: [PATCH RFC 3/3] xen: Introduce a platform sub-op to retrieve the VGA information

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Mon, Feb 07, 2022 at 09:57:55AM +0100, Jan Beulich wrote:
> On 06.02.2022 20:28, Julien Grall wrote:
> > From: Julien Grall <jgrall@xxxxxxxxxx>
> > 
> > When using EFI, the VGA information is fetched using the EFI
> > boot services. However, Xen will have exited the boot services.
> > Therefore, we need to find a different way to pass the information
> > to dom0.
> > 
> > For PV dom0, they are part of the start_info. But this is not
> > something that exists on Arm. So the best way would to be to
> > use a hypercall.
> > 
> > For now the structure layout is based on dom0_vga_console_info
> > for convenience. I am open on another proposal.
> > 
> > Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>
> 
> Cc-ing Roger as this may want using for PVH Dom0 also on x86; my
> first attempt to propagate this information was rejected.

I think it's easier to use a Xen specific layout in XENPF, as that's
already a Xen specific interface.

I wonder however if passing the information here (instead of doing it
in the start info or equivalent) could cause a delay in the
initialization of the video console. I guess the same happens when
using the Xen consoles (either the hypercall one or the shared ring),
so it's fine.

> > --- a/xen/include/public/platform.h
> > +++ b/xen/include/public/platform.h
> > @@ -244,6 +244,7 @@ DEFINE_XEN_GUEST_HANDLE(xenpf_efi_runtime_call_t);
> >  #define  XEN_FW_EFI_PCI_ROM        5
> >  #define  XEN_FW_EFI_APPLE_PROPERTIES 6
> >  #define XEN_FW_KBD_SHIFT_FLAGS    5
> > +#define XEN_FW_VGA_INFO           6
> 
> Perhaps s/VGA/VIDEO/, despite ...
> 
> >  struct xenpf_firmware_info {
> >      /* IN variables. */
> >      uint32_t type;
> > @@ -311,6 +312,7 @@ struct xenpf_firmware_info {
> >  
> >          /* Int16, Fn02: Get keyboard shift flags. */
> >          uint8_t kbd_shift_flags; /* XEN_FW_KBD_SHIFT_FLAGS */
> > +        struct dom0_vga_console_info vga;
> 
> ... the structure name including "vga" (but if the #define is adjusted,
> the field name would want to become "video" as well).

It's my understanding that this will forcefully be
XEN_VGATYPE_EFI_LFB, at which point we could consider giving a type
name to the vesa_lfb field of dom0_vga_console_info (video_lfb) and
use the same struct here?

There's no need to propagate XEN_VGATYPE_TEXT_MODE_3 into this
interface.

Thanks, Roger.