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 [off-list ref] wrote:

quoted

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.  :-(

quoted

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