From mboxrd@z Thu Jan 1 00:00:00 1970 From: Srinivas Pandruvada Subject: Re: [PATCH] i2c: Add generic support passing secondary devices addresses Date: Wed, 15 Oct 2014 11:54:37 -0700 Message-ID: <1413399277.1902.51.camel@spandruv-desktop.jf.intel.com> References: <1409925739-28188-1-git-send-email-jean-michel.hautbois@vodalys.com> <20140922104555.GQ1786@lahna.fi.intel.com> <542023C8.8080802@metafoo.de> <20140922134535.GZ1786@lahna.fi.intel.com> <54202E28.80500@metafoo.de> <20140922144144.GF1786@lahna.fi.intel.com> <20141003104637.GC1349@katana> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20141003104637.GC1349@katana> Sender: linux-i2c-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Wolfram Sang Cc: Mika Westerberg , Lars-Peter Clausen , Jean-Michel Hautbois , linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, mark.rutland-5wv7dgnIgG8@public.gmane.org List-Id: linux-i2c@vger.kernel.org Hi Lars and Jean, Are you taking this patch further to take care about ACPI related stuff submitted by Mika? Thanks, Srinivas On Fri, 2014-10-03 at 12:46 +0200, Wolfram Sang wrote: > > > Ok, looks like there are two main differences in the two implementations. > > > > > > 1) The ACPI one uses a integer index and the DT one uses a string index to > > > lookup the device. > > > > > > The problem with the index lookup is that the order is binding specific. So > > > it might be different between e.g. the devicetree binding and the ACPI > > > binding. This makes it quite hard to use the API in a generic way and you'd > > > end up with hacks like: > > > > > > if (client->dev.of_node) > > > index = 3; > > > else if (ACPI_COMPANION(client->dev)) > > > index = 1; > > > else > > > index = 5; > > > > > > > Indeed. > > > > > So we might need a extra translation table which maps a name to a ACPI index > > > and then we could use the name as the generic index in the driver. > > > > Good thing is that ACPI 5.1 _DSD finally allows us to use similar naming > > as the DT has been doing. Problem is that we need to support both the > > new way *and* the older index lookup somehow :-/ > > > > > 2) The ACPI implementation returns the i2c_board_info and the adapter, while > > > the DT implementation returns the instantiated I2C client device. > > > > > > It might make sense to have both. I image that most drivers are just > > > interested in creating a new client device and will simply pass the board > > > info and adapter they got to i2c_new_device(). In this case it makes sense > > > to have a helper function which already does this internally to avoid > > > boilerplate code duplication. > > > > I agree. How about making that helper a wrapper around the function that > > returns both i2c_board_info and an adapter? > > > > > There will probably some special cases though in which case the driver wants > > > to get the adapter and the board info and then manually call > > > i2c_new_device() after having done some additional steps. > > > > Yes, if the alternative address happens to be on another bus. That > > should at least be possible with this API. > > Thanks for the discussion so far! I'll wait and see if some patches come > out of it and mark this one as deferred for now. >