[PATCH 3.9 1/3] misc: new driver for GPIO-connected 7-segment displays

[arnd@arndb.de (Arnd Bergmann)]

On Monday 07 January 2013, Thomas Petazzoni wrote:
> Dear Arnd Bergmann,
> 
> On Mon, 7 Jan 2013 19:43:39 +0000, Arnd Bergmann wrote:
> 
> > >  .../devicetree/bindings/misc/gpio-7seg.txt         |   18 +++
> > >  drivers/misc/Kconfig                               |   13 ++
> > >  drivers/misc/Makefile                              |    1 +
> > >  drivers/misc/gpio-7seg.c                           |  168 ++++++++++++++++++++
> > 
> > I wonder if it would make sense to merge this into the LED subsystem
> > rather than having it as a standalone driver.
> 
> Hum, maybe. How do you see it fitting inside the LED subsystem? The
> purpose of the device is quite different in its userspace to kernel
> interface, no?

The LED subsystem can be used by both in-kernel and by user space
front-ends. It currently supports on/off, blinking and variable
brightness LEDs. Adding 7-segment LEDs may be a stretch but also
would fit into the same basic interface I think.

In addition, it would not have to be GPIO based, although that may
be the only implementation we need for the foreseeable future.
Well, unless you make a driver for PC-style "port-0x80" PCI
cards.


> > > +	sdev->dev_attr.attr.name = "value";
> > > +	sdev->dev_attr.attr.mode = S_IRUGO | S_IWUGO;
> > > +	sdev->dev_attr.show = gpio_7seg_show;
> > > +	sdev->dev_attr.store = gpio_7seg_store;
> > 
> > Any reason why you are not using the DEVICE_ATTR macro?
> 
> DEVICE_ATTR declares the structure, and I wanted one per gpio_7seg
> device, which is dynamically allocated, so I thought that using
> DEVICE_ATTR was not possible. But now that you point this, I realize
> that I was stupid. I can perfectly live with one single global 'struct
> device_attribute' that I register to several devices using
> device_create_file(), no?

Correct.

> That said, is it worth the effort to continue polishing this driver,
> after seeing the feedback from Greg about it? I don't mind working on
> it more and fix the problems of course, but if the general answer is
> that we don't want such a driver in the kernel, then I'd better not
> spend more time on this.

I only saw the discussion after I had sent my reply. I think that
this driver in the form of a drivers/misc sysfs driver is not worth
pursuing, but it may still be possible to integrate it nicely into
the LED framework.

	Arnd