Re: [PATCH/RFC v2] [SCSI] atp870u: Fix bad use of udelay

[Andrew Morton <akpm@linux-foundation.org>]

On Tue, 24 Apr 2012 02:49:16 -0500
Jonathan Nieder <jrnieder@gmail.com> wrote:

> From: Martin Michlmayr <tbm@cyrius.com>
> 
> The ACARD driver calls udelay() with a value > 2000, which leads to
> to the following compilation error on ARM:
>   ERROR: "__bad_udelay" [drivers/scsi/atp870u.ko] undefined!
>   make[1]: *** [__modpost] Error 1
>
> ...
>
> --- a/drivers/scsi/atp870u.c
> +++ b/drivers/scsi/atp870u.c
> @@ -1173,7 +1173,16 @@ wait_io1:
>  	outw(val, tmport);
>  	outb(2, 0x80);
>  TCM_SYNC:
> -	udelay(0x800);
> +	/*
> +	 * The funny division into multiple delays is to accomodate
> +	 * arches like ARM where udelay() multiplies its argument by
> +	 * a large number to initialize a loop counter.  To avoid
> +	 * overflow, the maximum supported udelay is 2000 microseconds.
> +	 *
> +	 * XXX it would be more polite to find a way to use msleep()
> +	 */
> +	mdelay(2);
> +	udelay(48);
>  	if ((inb(tmport) & 0x80) == 0x00) {	/* bsy ? */
>  		outw(0, tmport--);
>  		outb(0, tmport);

Fair enough, I say.  Looking at this driver, I do think it's best to
minimally fix the build and then tiptoe away very delicately lest
something explode.

That being said, I'm glad the kernel has a function called "fun_scam".