On 5/18/22 20:48, Dexuan Cui wrote:

quoted

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.

Thanks for the review, Dexuan!

I've applied this patch now to the fbdev git tree.

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.

Haiyang, can you check that as well and send another patch for
the drm tree ?

Helge