From: Dexuan Cui <decui@microsoft.com>
Sent: Wednesday, May 4, 2022 10:05 AM
To: Haiyang Zhang <haiyangz@microsoft.com>; Wei Liu <wei.liu@kernel.org>;

quoted

...
When I initially implemented this driver 10 years ago, I believe there
was smaller limit for the fb... But I think this patch is good for the
newer MMIO alloc scheme. I hope to see reviews also from
 @Dexuan Cui @Michael Kelley (LINUX) who are more familiar with
the PCI/BAR/MMIO area.

Thanks,
- Haiyang

The patch looks good to me but I suggest we check with the Hyper-V
team to figure out how a Gen1 Windows VM supports a higher
resolution that needs a VRAM size of more than 64MB. Just in case we
miss something..

Thanks,
-- Dexuan

Reviewed-by: Dexuan Cui <decui@microsoft.com>

Saurabh checked this with Hyper-V team, who said there is no
Generation 1-specific block for larger VRAM sizes in Windows VM.

When the driver was originally developed, we didn't have the API
vmbus_allocate_mmio(), and I guess we just used the PCI device's BAR
address for simplicity, and didn't realize the restriction with very high
resolutions that require >64 MB VRAM. It looks like the synthetic
VMBus framebuffer device doesn't have to use the same MMIO range
used by the Hyper-V legacy PCI framebuffer device, so the patch
looks good to me.

BTW, please check the hyperv-drm driver as well:
drivers/gpu/drm/hyperv/hyperv_drm_drv.c
I think we should make the same change there to support 7680x4320
for Gen1 VMs.

Thanks,
Dexuan