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SubjectRe: [PATCH] vga16fb: refuse to load in face of other driver controlling primary card
On Tue, 20 Jul 2010 21:19:23 +0200
Marcin Slusarz <marcin.slusarz@gmail.com> wrote:

> We don't want vga16fb to mess with hardware initialized by other driver.
> Detect it and refuse to load.
> It fixes nouveau interrupt storm on some machines.
>
> Signed-off-by: Marcin Slusarz <marcin.slusarz@gmail.com>
> ---
> drivers/video/vga16fb.c | 13 ++++++++++++-
> 1 files changed, 12 insertions(+), 1 deletions(-)
>
> diff --git a/drivers/video/vga16fb.c b/drivers/video/vga16fb.c
> index 28ccab4..4505446 100644
> --- a/drivers/video/vga16fb.c
> +++ b/drivers/video/vga16fb.c
> @@ -22,6 +22,7 @@
> #include <linux/platform_device.h>
> #include <linux/screen_info.h>
>
> +#include <asm/fb.h>
> #include <asm/io.h>
> #include <video/vga.h>
>
> @@ -1415,7 +1416,7 @@ static struct platform_device *vga16fb_device;
>
> static int __init vga16fb_init(void)
> {
> - int ret;
> + int ret, i;
> #ifndef MODULE
> char *option = NULL;
>
> @@ -1424,6 +1425,16 @@ static int __init vga16fb_init(void)
>
> vga16fb_setup(option);
> #endif
> + for (i = 0 ; i < FB_MAX; i++) {
> + if (!registered_fb[i])
> + continue;
> + if (fb_is_primary_device(registered_fb[i])) {
> + printk(KERN_INFO "vga16fb: %s is driving the primary card, refusing to load\n",
> + registered_fb[i]->fix.id);
> + return -EBUSY;
> + }
> + }
> +
> ret = platform_driver_register(&vga16fb_driver);
>
> if (!ret) {

This seems pretty hacky, and specific to vga16fb.

Is vga16fb.c the only fbdev driver (now and forever more) which can
grab the hardware from under a different driver's feet?


This is the basic and very common problem of two drivers diddling the
same hardware, yes? A common way of preventing such collisions is to
perform a suitably-checked request_region() in both drivers. Whichever
driver gets there second will get a failure and will bale out cleanly.
Can that mechanism be made to work in this case?




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