linux-kernel - Re: [RFC][PATCH] regmap: make REGCACHE_NONE maps return error on regcache_sync

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Date:	Mon, 8 Jun 2015 15:16:41 +0100
From:	Nariman Poushin <nariman@...nsource.wolfsonmicro.com>
To:	Mark Brown <broonie@...nel.org>
Cc:	patches@...nsource.wolfsonmicro.com, linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH] regmap: make REGCACHE_NONE maps return error on
	regcache_sync

On Fri, May 08, 2015 at 11:34:54AM +0100, Nariman Poushin wrote:
> On Fri, May 08, 2015 at 11:20:19AM +0100, Mark Brown wrote:
> > On Fri, May 08, 2015 at 10:55:37AM +0100, Nariman Poushin wrote:
> > > Signed-off-by: Nariman Poushin <nariman@...nsource.wolfsonmicro.com>
> > > ---
> > >  regcache currently causes a BUG_ON if cache_sync/sync_region is
> > >  called on a map with cache_type REGCACHE_NONE. This is not
> > >  consistent with the behaviour of regcache_read/write which
> > >  currently just return -ENOSYS and only throws a BUG_ON if
> > >  the cache_type is something that _should_ have cache ops,
> > >  but doesn't. Sure your device might not work, it but doesn't
> > >  seem right to panic the kernel. The other option I suppose
> > >  is to change it to a WARN_ON.
> > 
> > Please submit patches in the format covered in SubmittingPatches, the
> > changelog goes before the signoff.  
> >
> 
> Will do, apologies.
>  
> > The reason this is so loud is that while it's reasonable that generic
> > code could end up triggering a write it's difficult to see any way in
> > which a sync could be triggered on a device without a cache without it
> > being an obvious bug.  Since people frequently don't bother checking
> > return codes loud log messages are our only real way of reporting this,
> > given where syncs tend to happen it's not likely to happen in an obscure
> > code path that won't get seen.
> 
> Fair enough, that makes sense.

In light of this:
https://lkml.org/lkml/2015/6/7/193

Would it be prudent to now  make these WARN_ON? It seems like it's not
worth taking the kernel down in the case where you are trying to sync to
a non-existent cache for a peripheral. Of course it could be that the 
particular write _not_ going in to the cache is catastrophic for some
other reason, but it still seems a bit severe and given the discussion
above not the intended usage for BUG_ON. It doesn't feel like this
satisfies the test:

"The *ONLY* acceptable reason for a BUG_ON() is if the machine is dead
anyway because of some major internal corruption."

Anyway, just a thought. Not sure if this constitutes a "content-less
bump", I just read something that I thought may change our previous
assumptions, if it does, apologies.

Thanks
Nariman
> 
> Thanks
> Nariman
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