[RFC/RFT] ssb: Avoid system hang when SPROM read fails

[John W. Linville]

On Sun, Apr 25, 2010 at 05:30:28PM -0500, Larry Finger wrote:
> In kernel Bugzilla #15825, the OP reports a case of intermittent reading
> of the SPROM. If such reads fail, the box hangs. Thanks to careful testing
> by bugzillakernelorg at lez.ath.cx has shown that the first read of the
> SPROM returns 0xFFFF with the hang happening on the next read.
> 
> The source of the read failure is still under investigation; however,
> this patch does avoid the system hang.
> 
> Signed-off-by: Larry Finger <Larry.Finger at lwfinger.net>
> ---
> 
> John,
> 
> Does this patch avoid the system hang on your box?
> 
> Larry
> ---
> 
> ===================================================================
> --- wireless-testing.orig/drivers/ssb/pci.c
> +++ wireless-testing/drivers/ssb/pci.c
> @@ -253,6 +253,11 @@ static int sprom_do_read(struct ssb_bus
>  {
>  	int i;
>  
> +	/* Check if SPROM can be read */
> +	if (ioread16(bus->mmio + SSB_SPROM_BASE) == 0xFFFF) {
> +		ssb_printk(KERN_ERR PFX "Unable to read SPROM\n");
> +		return -ENODEV;
> +	}
>  	for (i = 0; i < bus->sprom_size; i++)
>  		sprom[i] = ioread16(bus->mmio + SSB_SPROM_BASE + (i * 2));
>  

Well, the "good" news is that I hit the "Unable to read SPROM" case.
The bad news is that the box still hangs after the -ENODEV.  I have
not yet tracked-down the exact location of the current hang.

John

P.S.  Sorry about the 'radio silence' -- I've been distracted with
some other things.  Also, the box in question originally belonged
to someone else who had configured it in a way that was less than
friendly to kernel development.  I finally reinstalled it...
-- 
John W. Linville		Someday the world will need a hero, and you
linville at tuxdriver.com			might be all we have.  Be ready.