linux-kernel - Re: [PATCH V4 1/2] ACPI / EC: Fix broken 64bit big-endian users of 'global

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Message-ID: <1443206945.2161.9.camel@sipsolutions.net>
Date:	Fri, 25 Sep 2015 20:49:05 +0200
From:	Johannes Berg <johannes@...solutions.net>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linaro-kernel@...ts.linaro.org,
	QCA ath9k Development <ath9k-devel@....qualcomm.com>,
	Intel Linux Wireless <ilw@...ux.intel.com>,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-acpi@...r.kernel.org,
	linux-bluetooth@...r.kernel.org, iommu@...ts.linux-foundation.org,
	netdev@...r.kernel.org, linux-wireless@...r.kernel.org,
	linux-scsi@...r.kernel.org, linux-usb@...r.kernel.org,
	linux-edac@...r.kernel.org, linux-mm@...ck.org,
	alsa-devel@...a-project.org
Subject: Re: [PATCH V4 1/2] ACPI / EC: Fix broken 64bit big-endian users of
 'global_lock'


> Rafael wrote:
> > Actually, what about adding a local u32 variable, say val, here and 
> > doing
> > 
> > >  	if (!debugfs_create_x32("gpe", 0444, dev_dir, (u32 
> > > *)&first_ec->gpe))
> > >  		goto error;
> > >  	if (!debugfs_create_bool("use_global_lock", 0444, 
> > > dev_dir,
> > > -				 (u32 *)&first_ec->global_lock))
> > > +				 &first_ec->global_lock))
> > 
> > 	if (!debugfs_create_bool("use_global_lock", 0444, dev_dir, 
> > &val))
> > 
> > >  		goto error;
> > 
> > 	first_ec->global_lock = val;
> > 
> > And then you can turn val into bool just fine without changing the 
> > structure
> > definition.

Ok, then, but that means Rafael is completely wrong ...
debugfs_create_bool() takes a *pointer* and it needs to be long-lived,
it can't be on the stack. You also don't get a call when it changes.

If you cannot change the struct definition then you must implement a
debugfs file with its own read/write handlers.

johannes
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