[PATCH v2] fbdev: arkfb: Request legacy VGA I/O region

[PATCH v2] fbdev: arkfb: Request legacy VGA I/O region

[Swaraj Gaikwad]

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.

Fix this by using devm_request_region() during the probe function.
This ensures the region is properly reserved and automatically released
on driver detach.

v1: https://lore.kernel.org/lkml/20251213154937.104301-1-swarajgaikwad1925@gmail.com/
Signed-off-by: Swaraj Gaikwad <swarajgaikwad1925@gmail.com>
---
v2:
 - Use resource_size(&vga_res) instead of hardcoded 64 * 1024.
 - (Feedback from Kees Cook)

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, resource_size(&vga_res), "arkfb-vga")) {
+		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

Re: [PATCH v2] fbdev: arkfb: Request legacy VGA I/O region

[Sam Ravnborg]

Hi Swaraj,

On Sat, Dec 13, 2025 at 08:22:34PM +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.
> 
> Fix this by using devm_request_region() during the probe function.
> This ensures the region is properly reserved and automatically released
> on driver detach.
> 
> v1: https://lore.kernel.org/lkml/20251213154937.104301-1-swarajgaikwad1925@gmail.com/
> Signed-off-by: Swaraj Gaikwad <swarajgaikwad1925@gmail.com>
> ---
> v2:
>  - Use resource_size(&vga_res) instead of hardcoded 64 * 1024.
>  - (Feedback from Kees Cook)
> 
> 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, resource_size(&vga_res), "arkfb-vga")) {
> +		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;

Any explanation why devm_request_region() is the right choice here?
As per the line above vga_res.start is iomem, and I had expected to see
devm_request_mem_region() used.
I looked only briefly, so I may be wrong.

	Sam

Re: [PATCH v2] fbdev: arkfb: Request legacy VGA I/O region

[Swaraj Gaikwad]

Hi Sam,

Thanks for the review.

You are right that the cast to (void __iomem *) makes it look like memory,
but the resource is explicitly initialized as I/O ports a few lines earlier:

    vga_res.flags = IORESOURCE_IO;

Since the resource flag is IORESOURCE_IO (targeting the legacy VGA ports),
I used devm_request_region() instead of devm_request_mem_region().

Best regards,
Swaraj