From mboxrd@z Thu Jan 1 00:00:00 1970 From: Laurent Pinchart Subject: Re: [RFC] media DT bindings Date: Tue, 31 Jul 2012 14:08:29 +0200 Message-ID: <2642313.6bQqiyFNFL@avalon> References: <1537713.eFPuk01afu@avalon> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7Bit Return-path: In-Reply-To: Sender: linux-media-owner@vger.kernel.org To: Guennadi Liakhovetski Cc: Sylwester Nawrocki , Linux Media Mailing List , Magnus Damm , devicetree-discuss List-Id: devicetree@vger.kernel.org Hi Guennadi, On Tuesday 31 July 2012 11:26:27 Guennadi Liakhovetski wrote: > On Fri, 27 Jul 2012, Laurent Pinchart wrote: > > Hi Sylwester, > > > > On Wednesday 18 July 2012 19:00:15 Sylwester Nawrocki wrote: > > > On 07/16/2012 01:41 PM, Guennadi Liakhovetski wrote: > [snip] > > > > >>> An sh-mobile CEU DT node could look like > > > >>> > > > >>> ceu0@0xfe910000 = { > > > >>> > > > >>> compatible = "renesas,sh-mobile-ceu"; > > > >>> reg =<0xfe910000 0xa0>; > > > >>> interrupts =<0x880>; > > > >>> bus-width =<16>; /* #lines routed on the board */ > > > >>> clock-frequency =<50000000>; /* max clock */ > > > >>> #address-cells =<1>; > > > >>> #size-cells =<0>; > > > >>> ... > > > >>> ov772x-1 = { > > > >>> > > > >>> reg =<0>; > > > > > > This property might be redundant, we already have the "client" phandle > > > pointing to "ov772x@0x21-0", which has all interesting properties inside > > > it. Other than there is probably no reasonable usage for it under > > > "ceu0@0xfe910000" node ? > > > > > > >>> client =<&ov772x@0x21-0>; > > > >>> local-pad = "parallel-sink"; > > > >>> remote-pad = "parallel-source"; > > > >> > > > >> I'm not sure I like that. Is it really needed when we already have > > > >> the child/parent properties around ? > > > > > > > > I think it is. Both the host and the client can have multiple pads > > > > (e.g., > > > > parallel / serial). These properties specify which pads are used and > > > > make > > > > the translation between DT data and our subdev / pad APIs simpler. > > > > > > OK, sorry, but isn't it all about just specifying what sort of data bus > > > is used ? :-) > > > > In some (many/most ?) cases probably, but not in all of them. > > > > What about merging the client and remote-pad properties ? The resulting > > property would then reference a pad with <&ov772x@0x21-0 0>. > > What would the "0" parameter mean then? Pad #0? Yes. > But aren't these numbers device specific? Maybe not a huge deal, but these > numbers are defind by the driver, right? Not the DT itself. So, drivers then > will have to take care not to change their pad numbering. Whereas using > strings, we can fix strings in the common V4L DT spec and keep them standard > across devices and drivers. Then drivers might be less likely to change > these assignments randomly ;-) Userspace applications usually rely on pad numbers as well, so I consider them as more or less part of the ABI. If we really need to, we could add a DT pad number -> media controller pad number conversion in the driver, that would be less expensive than pad name -> pad number conversion (especially since it would be skipped in most cases). > [snip] > > > > I'd like just to point one detail here, as sensor subdev drivers control > > > their voltage regulators and RESET/STANDBY (gpio) signals, they should > > > also be able to control the master clock. In order to ensure proper > > > power > > > up/down sequences. It is a bad practice to enable clocks before voltage > > > supplies are switched on and we shouldn't have that as a general > > > assumption at the kernel frameworks. > > > > > > One possible solution would be to have host/bridge drivers to register > > > a clkdev entry for I2C client device, so it can acquire the clock > > > through > > > just clk_get(). We would have to ensure the clock is not tried to be > > > accessed before it is registered by a bridge. This would require to add > > > clock handling code to all sensor/encoder subdev drivers though.. > > > > I thik it's a good practice to add clock management to subdevs anyway, and > > the common clock framework should make that easy (or at least not too > > difficult). We can migrate subdevs one by one as we add DT support for > > them. > > Yes, this would be good. -- Regards, Laurent Pinchart