linux-kernel - Re: [PATCH] video: hyperv_fb: Allow resolutions with size

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Message-ID: <20220428143746.sya775ro5zi3kgm3@liuwe-devbox-debian-v2>
Date:   Thu, 28 Apr 2022 14:37:46 +0000
From:   Wei Liu <wei.liu@...nel.org>
To:     Saurabh Sengar <ssengar@...ux.microsoft.com>
Cc:     ssengar@...rosoft.com, kys@...rosoft.com, haiyangz@...rosoft.com,
        sthemmin@...rosoft.com, wei.liu@...nel.org, decui@...rosoft.com,
        deller@....de, linux-hyperv@...r.kernel.org,
        linux-fbdev@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] video: hyperv_fb: Allow resolutions with size > 64 MB
 for Gen1

On Wed, Apr 27, 2022 at 06:47:53AM -0700, Saurabh Sengar wrote:
> This patch fixes a bug where GEN1 VMs doesn't allow resolutions greater
> than 64 MB size (eg 7680x4320). Unnecessary PCI check limits Gen1 VRAM
> to legacy PCI BAR size only (ie 64MB). Thus any, resolution requesting
> greater then 64MB (eg 7680x4320) would fail. MMIO region assigning this
> memory shouldn't be limited by PCI bar size.
> 
> Signed-off-by: Saurabh Sengar <ssengar@...ux.microsoft.com>
> ---
>  drivers/video/fbdev/hyperv_fb.c | 19 +------------------
>  1 file changed, 1 insertion(+), 18 deletions(-)
> 
> diff --git a/drivers/video/fbdev/hyperv_fb.c b/drivers/video/fbdev/hyperv_fb.c
> index c8e0ea2..58c304a 100644
> --- a/drivers/video/fbdev/hyperv_fb.c
> +++ b/drivers/video/fbdev/hyperv_fb.c
> @@ -1009,7 +1009,6 @@ static int hvfb_getmem(struct hv_device *hdev, struct fb_info *info)
>  	struct pci_dev *pdev  = NULL;
>  	void __iomem *fb_virt;
>  	int gen2vm = efi_enabled(EFI_BOOT);
> -	resource_size_t pot_start, pot_end;
>  	phys_addr_t paddr;
>  	int ret;
>  
> @@ -1060,23 +1059,7 @@ static int hvfb_getmem(struct hv_device *hdev, struct fb_info *info)
>  	dio_fb_size =
>  		screen_width * screen_height * screen_depth / 8;
>  
> -	if (gen2vm) {
> -		pot_start = 0;
> -		pot_end = -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?

Thanks,
Wei.

> -		}
> -
> -		pot_end = pci_resource_end(pdev, 0);
> -		pot_start = pot_end - screen_fb_size + 1;
> -	}
> -
> -	ret = vmbus_allocate_mmio(&par->mem, hdev, pot_start, pot_end,
> +	ret = vmbus_allocate_mmio(&par->mem, hdev, 0, -1,
>  				  screen_fb_size, 0x100000, true);
>  	if (ret != 0) {
>  		pr_err("Unable to allocate framebuffer memory\n");
> -- 
> 1.8.3.1
>