Hello Rob, > > >> On Monday 05 Dec 2016 09:57:32 Rob Herring wrote: > > >> > On Mon, Dec 5, 2016 at 8:40 AM, Laurent Pinchart wrote: > > >> > > On Monday 05 Dec 2016 08:18:34 Rob Herring wrote: > > >> > >> On Fri, Nov 25, 2016 at 10:55 AM, Ramesh Shanmugasundaram wrote: > > >> > >>> Hello DT maintainers, > > >> > >>> > > >> > >>> In one of the Renesas SoCs we have a device called DRIF > > >> > >>> (Digital Radio > > >> > >>> Interface) controller. A DRIF channel contains 4 external > > >> > >>> pins > > >> > >>> - SCK, SYNC, Data pins D0 & D1. > > >> > >>> > > >> > >>> Internally a DRIF channel is made up of two SPI slave devices > > >> > >>> (also called sub-channels here) that share common CLK & SYNC > > >> > >>> signals but have their own resource set. The DRIF channel can > > >> > >>> have either one of the sub-channel active at a time or both. > > >> > >>> When both sub-channels are active, they need to be managed > > >> > >>> together as one device as they share same CLK & SYNC. We plan > > >> > >>> to tie these two sub-channels together with a new property > > >> > >>> called > > "renesas,bonding". > > >> > >> > > >> > >> Is there no need to describe the master device? No GPIOs, > > >> > >> regulators or other sideband controls needed? If that's never > > >> > >> needed (which seems doubtful), then I would do something > > >> > >> different here probably with the master device as a child of > > >> > >> one DRIF and then phandles to master from the other DRIFs. > > >> > >> Otherwise, this looks > > >> fine to me. > > >> > > > > >> > > Here's a bit of background. > > >> > > > > >> > > The DRIF is an SPI receiver. It has three input pins, a clock > > >> > > line, a data line and a sync signal. The device is designed to > > >> > > be connected to a variety of data sources, usually plain SPI (1 > > >> > > data line), IIS (1 data > > >> > > line) but also radio tuners that output I/Q data > > >> > > (http://www.ni.com/tutorial/4805/en/) over two data lines. > > >> > > > > >> > > In the case of IQ each data sample is split in two I and Q > > >> > > values (typically 16 to 20 bits each in this case), and the > > >> > > values are transmitted serially over one data line each. The > > >> > > synchronization and clock signals are common to both data > > >> > > lines. The DRIF is optimized for this use case as the DRIF > > >> > > instances in the SoC (each of them having independent clocks, > > >> > > interrupts and control > > >> > > registers) are grouped by two, and the two instances in a group > > >> > > handle a single data line each but share the same clock and > > >> > > sync > > input. > > >> > > > > >> > > On the software side we need to group the I and Q values, which > > >> > > are DMA'ed to memory by the two DRIF instances, and make them > > >> > > available to userspace. The V4L2 API used here in SDR (Software > > >> > > Defined Radio) mode supports such use cases and exposes a > > >> > > single device node to userspace that allows control of the two > > >> > > DRIF instances as a single device. To be able to implement this > > >> > > we need kernel code to be aware of DRIF groups and, while > > >> > > binding to the DRIF instances separately, expose only one V4L2 > > >> > > device to > > userspace for each group. > > >> > > > > >> > > There's no master or slave instance from a hardware point of > > >> > > view, but the two instances are not interchangeable as they > > >> > > carry separate > > >> information. > > >> > > They must thus be identified at the driver level. > > >> > > > >> > By master, I meant the external master device that generates the > > >> > IQ data, not which of the internal DRIF blocks is a master of the > other. > > >> > So back to my question, does the external master device need to > > >> > be described? I worry the answer now for a simple case is no, but > > >> > then later people are going to have cases needing to describe > > >> > more. We need to answer this question first before we can decide > > >> > what this binding should look like. > > >> > > >> Oh yes the external device certainly needs to be described. As it > > >> is controlled through a separate, general-purpose I2C or SPI > > >> controller, it should be a child node of that controller. The DRIF > > >> handles the data interface only, not the control interface of the > external device. > > > > > > Yes, as Laurent mentioned, the external master will be described > > separately. The data interface with the master is described through > > port nodes. E.g. > > > > > > port { > > > drif0_ep: endpoint { > > > remote-endpoint = <&tuner_ep>; > > > }; > > > }; > > > > > > Do we agree on this model please? > > > > Well, that's not complete as you should have both DRIF0 and DRIF1 > > having connections to the tuner. Then you can walk the graph and find > > everything, and you then don't need the bonding property. > > Assuming the third party tuner exposes it's two data lines as two > endpoints, it seems possible with of_graph.h apis to walk through tuner > end points and get the phandle of the other DRIF device. However, there > are couple of points coming to mind. > > - The ctrl pins shared between two DRIFs needs to be enabled in one of the > DRIF device. Do we choose this device arbitrarily? Do we expose the CTRL > signal properties (msb/lsb first, polarity etc) on both DRIF devices? > Should we think about scalability? > > - It mandates the third party tuner device to expose it's two data lines > as two endpoints. It assumes that a single third party master device > controls both the data lines coming to each DRIF device. > > The bonding property looks a bit cleaner on these aspects because it > describes only the DRIF device. Shall we please conclude on the model? Are you happy with the use of "renesas,bonding" property if the concern is on pushing this as a generic property? I would appreciate your feedback. Thanks, Ramesh
