linux-kernel - Re: [PATCH] fbdev: arkfb: Request legacy VGA I/O region

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Message-ID: <202512130621.7FE2C04639@keescook>
Date: Sat, 13 Dec 2025 06:22:00 -0800
From: Kees Cook <kees@...nel.org>
To: Swaraj Gaikwad <swarajgaikwad1925@...il.com>
Cc: Helge Deller <deller@....de>, Andrew Morton <akpm@...ux-foundation.org>,
	Hans Verkuil <hverkuil+cisco@...nel.org>, Zi Yan <ziy@...dia.com>,
	Frank Li <Frank.Li@....com>, Bjorn Andersson <andersson@...nel.org>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Qianfeng Rong <rongqianfeng@...o.com>,
	Vivek Kasireddy <vivek.kasireddy@...el.com>,
	Konrad Dybcio <konrad.dybcio@....qualcomm.com>,
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>,
	"open list:FRAMEBUFFER LAYER" <linux-fbdev@...r.kernel.org>,
	"open list:FRAMEBUFFER LAYER" <dri-devel@...ts.freedesktop.org>,
	open list <linux-kernel@...r.kernel.org>, skhan@...uxfoundation.org,
	david.hunter.linux@...il.com
Subject: Re: [PATCH] fbdev: arkfb: Request legacy VGA I/O region

On Sat, Dec 13, 2025 at 03:49:32PM +0000, Swaraj Gaikwad wrote:
> The arkfb driver uses the legacy VGA I/O range (0x3c0+) but does not
> request it. This can cause conflicts with other drivers that try to
> reserve these ports.

Eek, nice catch!

> 
> Fix this by using devm_request_region() during the probe function.
> This ensures the region is properly reserved and automatically released
> on driver detach.
> 
> Signed-off-by: Swaraj Gaikwad <swarajgaikwad1925@...il.com>
> ---
> Compile-tested only on x86_64.
> 
>  drivers/video/fbdev/arkfb.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/video/fbdev/arkfb.c b/drivers/video/fbdev/arkfb.c
> index ec084323115f..24e4c20d1a32 100644
> --- a/drivers/video/fbdev/arkfb.c
> +++ b/drivers/video/fbdev/arkfb.c
> @@ -1018,6 +1018,12 @@ static int ark_pci_probe(struct pci_dev *dev, const struct pci_device_id *id)
> 
>  	pcibios_bus_to_resource(dev->bus, &vga_res, &bus_reg);
> 
> +	if (!devm_request_region(&dev->dev, vga_res.start, 64 * 1024, "arkfb-vga")) {

I was expecting to see vga_res.end as the third argument instead of
repeating the open-coded value.

-Kees

> +		dev_err(info->device, "cannot reserve legacy VGA ports\n");
> +		rc = -EBUSY;
> +		goto err_find_mode;
> +	}
> +
>  	par->state.vgabase = (void __iomem *) (unsigned long) vga_res.start;
> 
>  	/* FIXME get memsize */
> 
> base-commit: a859eca0e4cc96f63ff125dbe5388d961558b0e9
> --
> 2.52.0
> 

-- 
Kees Cook