Re: About devm_ioremap_resource()

[Jarkko Sakkinen <jarkko.sakkinen-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>]

On Wed, Feb 03, 2016 at 05:31:08PM -0700, Jason Gunthorpe wrote:
> On Wed, Feb 03, 2016 at 02:55:19PM -0800, Jarkko Sakkinen wrote:
> > Hi
> > 
> > I have couple of concerns with tpm_crb changes made for 4.5:
> > 
> > * I used devm_ioremap_nocache() to disable WB. This does not
> >   matter when one has ACPI start as it goes through SMM and caches are
> >   flushed. It might be a problem with a CRB start only TPM device. How does
> >   devm_ioremap_resource address this?
> 
> ioremap_nocache and ioremap() are the same thing, the former is just
> more descriptive.
> 
> devm_ioremap_resource calls ioremap which does ioremap_nocache.
> 
> Resources are assumed to be memory mapped registers, and are always
> handled appropriately.
> 
> > * I'm a bit puzzled with that function. Why there exists ioremaps that
> >   do not add stuff to a resource tree and those that do? Maybe you have
> >   a deeper understanding in this area could enlighten me since you did
> >   the commit.
> 
> The resource tree and mapping are different things, not all drivers
> can use the resource tree all the time, but certainly the majority of
> drivers should be using it, hence the devm helper to do both.
> 
> When you see a ioremap without resource handling in a driver it is
> probably a mistake, and if it isn't, IMHO there should be a comment
> discussing why this driver cannot lock the resource region.

Thank you for clearing these out! I have nothing to add here. The
reason for two interfaces was what I expected...

> Jason

/Jarkko

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