Re: [rtc-linux] Re: [PATCH] Add support for pt7c4338 (rtc device) in rtc-ds1307 driver

[Anton Vorontsov <avorontsov@mvista.com>]

On Mon, May 30, 2011 at 02:29:58PM +0000, Tabi Timur-B04825 wrote:
> On Mon, May 30, 2011 at 3:24 AM, Wolfram Sang <w.sang@pengutronix.de> wrote:
> 
> > The first place where this should be mentioned is the datasheet of the
> > pt-chip, so you might ask the producer to add this information (don't
> > expect much to happen, though).
> 
> It's true that the data sheet does not mention that it's identical to
> the DS1307, but that's still no excuse for not noticing it and writing
> a whole driver for it.  :-(
> 
> > IIRC I asked you explicitly for the differences between the chips. If
> > there are none, you can use the driver directly, right? :)
> 
> Yes.  The device tree node for the PT7C4338 device should just say
> 
>    /* The board has a PT7C4338, which is compatible with the DS1307 */
>    compatible = "dallas,ds1307";

While it seems to be 100% compatible, there could be chip-specific
bugs or some interesting features that are hidden behind "reserved"
bits and registers.

So I think device tree should not lie about the chip model. Doing
'compatible = "pericom,pt7c4338", "dallas,ds1307"' is perfectly fine.

Note that today the several compatible entries approach gives you
almost nothing, as you will need to add pt7c4338 entry into the driver
anyway.

I tried to improve this, i.e. make linux do OF-matching on the most
generic compatible entry (the last one):

http://www.mail-archive.com/linuxppc-dev@lists.ozlabs.org/msg21196.html

It was received coldly though:

http://www.mail-archive.com/linuxppc-dev@lists.ozlabs.org/msg22041.html
http://www.mail-archive.com/linuxppc-dev@lists.ozlabs.org/msg21273.html

-- 
Anton Vorontsov
Email: cbouatmailru@gmail.com