From: Grant Likely <grant.likely@secretlab.ca>
To: Anton Vorontsov <avorontsov@mvista.com>
Cc: "a.zummo@towertech.it" <a.zummo@towertech.it>,
"rtc-linux@googlegroups.com" <rtc-linux@googlegroups.com>,
"p_gortmaker@yahoo.com" <p_gortmaker@yahoo.com>,
Jain Priyanka-B32167 <B32167@freescale.com>,
Tabi Timur-B04825 <B04825@freescale.com>,
"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>
Subject: Re: [rtc-linux] Re: [PATCH] Add support for pt7c4338 (rtc device) in rtc-ds1307 driver
Date: Fri, 3 Jun 2011 12:03:05 -0600 [thread overview]
Message-ID: <20110603180305.GF15616@ponder.secretlab.ca> (raw)
In-Reply-To: <20110530165745.GA2758@oksana.dev.rtsoft.ru>
On Mon, May 30, 2011 at 08:57:45PM +0400, Anton Vorontsov wrote:
> 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.
Correct. It's fine (and encouraged) to claim compatibility, but the
node should always specify the exact part in the compatible list.
>
> 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
On that note, device-tree-style of_match_table binding now works for
i2c devices, so the problems you were having with that thread should
now be solved.
The of_find_i2c_driver() approach was only ever a heuristic to get
things working in the short term. of_match_table is is better in the
long run.
g.
prev parent reply other threads:[~2011-06-03 18:03 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-05-26 7:03 [PATCH] Add support for pt7c4338 (rtc device) in rtc-ds1307 driver Priyanka Jain
2011-05-26 9:10 ` Wolfram Sang
2011-05-30 4:47 ` Jain Priyanka-B32167
2011-05-30 8:24 ` Wolfram Sang
2011-05-30 14:29 ` [rtc-linux] " Tabi Timur-B04825
2011-05-30 14:50 ` Wolfram Sang
2011-05-30 16:57 ` Anton Vorontsov
2011-06-03 18:03 ` Grant Likely [this message]
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