[PATCH] io-mapping: Indicate mapping failure

[Ruhl, Michael J]

>-----Original Message-----
>From: Andy Shevchenko <andriy.shevchenko at linux.intel.com>
>Sent: Tuesday, July 21, 2020 10:47 AM
>To: Ruhl, Michael J <michael.j.ruhl at intel.com>
>Cc: dri-devel at lists.freedesktop.org; Andrew Morton <akpm at linux-
>foundation.org>; Mike Rapoport <rppt at linux.ibm.com>; Chris Wilson
><chris at chris-wilson.co.uk>; stable at vger.kernel.org
>Subject: Re: [PATCH] io-mapping: Indicate mapping failure
>
>On Tue, Jul 21, 2020 at 10:16:41AM -0400, Michael J. Ruhl wrote:
>> Sometimes it is good to know when your mapping failed.
>
>Can you elaborate...

Sure, guess I was too glib. 😊

Currently  the io_mapping_init_wc (the !ATOMIC_IOMAP version), function will
always return success.

If the setting of the iomem (from ioremap_wc) fails, the only way for the 
caller to know is to check the value of iomap->iomem.

Since all of the callers expect a NULL return on error, and check for a NULL,
I felt this needed a fixes (i.e. unexpected behavior).

>> Fixes: cafaf14a5d8f ("io-mapping: Always create a struct to hold metadata
>about the io-mapping"
>
>...especially taking into account that Fixes implies regression / bug?

The failure (in my case a crash) is not revealed until the address is accessed
long after the init.

I will update the commit.

Mike

>--
>With Best Regards,
>Andy Shevchenko
>