[RFC/RFT PATCH] fbdev: q40fb: request memory region

[RFC/RFT PATCH] fbdev: q40fb: request memory region

[Sukrut Heroorkar]

The q40fb driver uses a fixed physical address but never reserves
the corresponding I/O region. Reserve the range  as suggested in
Documentation/gpu/todo.rst ("Request memory regions in all fbdev drivers").

If the memory cannot be reserved, fail probe with -EBUSY to avoid
conflicting with another user of the same address.

Signed-off-by: Sukrut Heroorkar <hsukrut3@gmail.com>
---
Testing: This patch is sent as RFT since Q40 hardware is unavilable and  
QEMU does not emulated a Q40 platform. The change is therefore compile-tested
only.

 drivers/video/fbdev/q40fb.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/video/fbdev/q40fb.c b/drivers/video/fbdev/q40fb.c
index 1ff8fa176124..7b5c31745041 100644
--- a/drivers/video/fbdev/q40fb.c
+++ b/drivers/video/fbdev/q40fb.c
@@ -101,6 +101,13 @@ static int q40fb_probe(struct platform_device *dev)
 	info->par = NULL;
 	info->screen_base = (char *) q40fb_fix.smem_start;
 
+	if (!request_mem_region(q40fb_fix.smem_start, q40fb_fix.smem_len,
+				"q40fb")) {
+		dev_err(&dev->dev, "cannot reserve video memory at 0x%lx\n",
+			q40fb_fix.smem_start);
+		return -EBUSY;
+	}
+
 	if (fb_alloc_cmap(&info->cmap, 256, 0) < 0) {
 		framebuffer_release(info);
 		return -ENOMEM;
-- 
2.43.0

Re: [RFC/RFT PATCH] fbdev: q40fb: request memory region

[Geert Uytterhoeven]

Hi Sukrut,

CC linux-m68k

On Thu, 20 Nov 2025 at 19:03, Sukrut Heroorkar <hsukrut3@gmail.com> wrote:
> The q40fb driver uses a fixed physical address but never reserves
> the corresponding I/O region. Reserve the range  as suggested in
> Documentation/gpu/todo.rst ("Request memory regions in all fbdev drivers").
>
> If the memory cannot be reserved, fail probe with -EBUSY to avoid
> conflicting with another user of the same address.
>
> Signed-off-by: Sukrut Heroorkar <hsukrut3@gmail.com>

Thanks for your patch!

> ---
> Testing: This patch is sent as RFT since Q40 hardware is unavilable and
> QEMU does not emulated a Q40 platform. The change is therefore compile-tested
> only.

I would suggest not to apply this, unless it is tested on real
hardware.  It wouldn't be the first time an innocent-looking change like
this breaks a system. See e.g.
https://lore.kernel.org/all/Y5I2oQexHNdlIbsQ@shell.armlinux.org.uk

> --- a/drivers/video/fbdev/q40fb.c
> +++ b/drivers/video/fbdev/q40fb.c
> @@ -101,6 +101,13 @@ static int q40fb_probe(struct platform_device *dev)
>         info->par = NULL;
>         info->screen_base = (char *) q40fb_fix.smem_start;
>
> +       if (!request_mem_region(q40fb_fix.smem_start, q40fb_fix.smem_len,
> +                               "q40fb")) {
> +               dev_err(&dev->dev, "cannot reserve video memory at 0x%lx\n",
> +                       q40fb_fix.smem_start);
> +               return -EBUSY;
> +       }
> +
>         if (fb_alloc_cmap(&info->cmap, 256, 0) < 0) {
>                 framebuffer_release(info);
>                 return -ENOMEM;

Gr{oetje,eeting}s,

                        Geert


--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds