linux-kernel - Re: [lm-sensors] [RFC PATCH 0/2] fs: sysfs: Add devres support

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Message-ID: <20130318132954.GA30482@roeck-us.net>
Date:	Mon, 18 Mar 2013 06:29:54 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Jean Delvare <khali@...ux-fr.org>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, lm-sensors@...sensors.org
Subject: Re: [lm-sensors] [RFC PATCH 0/2] fs: sysfs: Add devres support

On Mon, Mar 18, 2013 at 09:02:41AM +0100, Jean Delvare wrote:
> On Sun, 17 Mar 2013 06:19:33 -0700, Guenter Roeck wrote:
> > On Sun, Mar 17, 2013 at 01:39:20PM +0100, Jean Delvare wrote:
> > > I'd like to add something at this point.
> > > 
> > > We have historically created the hwmon attributes in the hardware (i2c,
> > > platform...) device, and then created an empty hwmon class device on
> > > top of it so that libsensors etc. can locate all hardware monitoring
> > > chips on the system. This is probably wrong and this may explain the
> > > difference of views between Greg and Guenter.
> > > 
> > > I suspect that ideally all hwmon-related attributes should belong to the
> > > hwmon-class device and not the physical device. Would doing so solve
> > > the problem of is_visible() needing chip-specific information that can
> > > only be gathered during probe()? Sure this is an interface change, but
> > > a few hwmon drivers already do it that way (the ones without an actual
> > > hardware device, e.g. ACPI thermal zones) and libsensors supports this
> > > since version 3.0.3, which was released in September 2008 - 4.5 years
> > > ago.
> > > 
> > > This would require creating the attributes after calling
> > > hwmon_device_register() rather than before, but from the ongoing
> > > discussion I seem to understand that the driver core supports creating
> > > the attributes for us, possibly at the same time as the class device
> > > will be created. Would this solve the userspace timing issue?
> > > 
> > This is what I had in mind as ultimate possibility when I created
> > the second API mentioned in my other e-mail.
> > 
> > struct device *devm_hwmon_device_register(struct device *dev,
> > 					  const struct attribute_group **groups)
> > 
> > The attributes are still attached to dev (ie to the hardware device)
> > in my current code, but it should be possible to attach them to the
> > hwmon class device instead.
> > 
> > Problem with that approach is that it makes drivers larger, not smaller,
> > at least if is_visible is needed. So it kind of defeats the purpose.
> > 
> > We can go along that route anyway if people think it is the right or a better
> > approach, but I am not sure if it is worth it. I can send out the patches if
> > there is interest.
> 
> Really, I don't know. All I know is that I do not have any time to
> devote to this ATM.
> 
Hi Jean,

Can't help it. Worst case I learned how make better use of is_visible
and how to avoid its pitfalls.

Guenter
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