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Date:   Thu, 19 May 2022 11:08:39 +0200
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Subject: Re: [PATCH] video: hyperv_fb: Allow resolutions with size > 64 MB for
 Gen1
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To:     Dexuan Cui <decui@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Wei Liu <wei.liu@kernel.org>,
        Saurabh Sengar <ssengar@linux.microsoft.com>,
        "Michael Kelley (LINUX)" <mikelley@microsoft.com>
Cc:     Saurabh Singh Sengar <ssengar@microsoft.com>,
        KY Srinivasan <kys@microsoft.com>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        "linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
        "linux-fbdev@vger.kernel.org" <linux-fbdev@vger.kernel.org>,
        "dri-devel@lists.freedesktop.org" <dri-devel@lists.freedesktop.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
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From:   Helge Deller <deller@gmx.de>
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On 5/18/22 20:48, Dexuan Cui wrote:
>> 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=
>;
>>> ...
>>> 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 hig=
h
> 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