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From:   Dexuan Cui <decui@microsoft.com>
To:     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>,
        "deller@gmx.de" <deller@gmx.de>,
        "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>
Subject: RE: [PATCH] video: hyperv_fb: Allow resolutions with size > 64 MB for
 Gen1
Thread-Topic: [PATCH] video: hyperv_fb: Allow resolutions with size > 64 MB
 for Gen1
Thread-Index: AQHYX9YSthbGf8K4qEaTeH9fJ7H5Eq0O8UBQ
Date:   Wed, 4 May 2022 17:05:05 +0000
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> From: Haiyang Zhang <haiyangz@microsoft.com>
> > > ...
> > > -	if (gen2vm) {
> > > -		pot_start =3D 0;
> > > -		pot_end =3D -1;
> > > -	} else {
> > > -		if (!(pci_resource_flags(pdev, 0) & IORESOURCE_MEM) ||
> > > -		    pci_resource_len(pdev, 0) < screen_fb_size) {
> > > -			pr_err("Resource not available or (0x%lx < 0x%lx)\n",
> > > -			       (unsigned long) pci_resource_len(pdev, 0),
> > > -			       (unsigned long) screen_fb_size);
> > > -			goto err1;
> >
> > This restriction has been in place since day 1. Haiyang, you wrote this
> > driver. Can you comment on whether this change here is sensible?
>=20
> 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.
>=20
> 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