On Mon, Sep 02, 2013 at 05:21:58PM +0100, Sylwester Nawrocki wrote: > Hi Mark, Hi Sylwester, > > On 08/27/2013 11:14 AM, Mark Rutland wrote: > >> +endpoint node > >> +------------- > >> + > >> +- data-lanes : (optional) specifies MIPI CSI-2 data lanes as covered in > >> + video-interfaces.txt. This property can be only used to specify number > >> + of data lanes, i.e. the array's content is unused, only its length is > >> + meaningful. When this property is not specified default value of 1 lane > >> + will be used. > > > > Apologies for having not replied to the last posting, but having looked > > at the documentation I was provided last time [1], I don't think the > > values in the data-lanes property should be described as unused. That > > may be the way the Linux driver functions at present, but it's not how > > the generic video-interfaces binding documentation describes the > > property. > > > > If the CSI transmitter hardware doesn't support logical remapping of > > lanes, then the only valid values for data-lanes would be a contiguous > > list of lane IDs starting at 1, ending at 4 at most. Valid values for > > the property would be one of: > > > > data-lanes = <1>; > > data-lanes = <1>, <2>; > > data-lanes = <1>, <2>, <3>; > > data-lanes = <1>, <2>, <3>, <4>; > > > > We can mention the fact the hardware doesn't support remapping of lanes, > > and therefore the list must start with lane 1 and end with (at most) > > lane 4. That way a dts will match the generic binding and actually > > describe the hardware, and it's possible for Linux (or any other OS) to > > factor out the parsing of data-lanes later as desired. > > > > I don't think we should offer freedom to encode garbage in the dt when > > we can just as easily encourage more standard use of bindings that will > > make our lives easier in the long-term. > > I entirely agree, that's a very accurate analysis. > > Presumably the data-lanes property's descriptions could be improved so > it is said explicitly that array elements 0...N - 1, where N = 4, > correspond to logical data lanes 1...N. That makes sense to me. > > Then considering the values in the data-lanes property, I didn't make > the description terribly specific about the fact that pool of indexes > 0...4 is used for the clock lane and 4 data lanes. The values could well > be H/W specific, but it seems more sensible to enforce common range. > It may not match exactly with documentation of various hardware. E.g. > OMAP, see page 1661, register CSI2_COMPLEXIO_CFG [1], uses indexes > 1..5 to indicate position of a data lane and 0 is used to mark a lane > as unused. Ah, I see. I guess this boils down to what the "physical indexes" referred to by the video-interfaces binding actually are. If an interface may only ever have 5 lanes, then using a logical index sounds fine. But if we ever have the case where a CSI transmitter has more than 5 lanes (so it could communicate with multiple receviers), then the value has to become hardware-specific. At that point, we'd possibly need to define remapping of the clocks too. I'm not that familiar with CSI so I'm not sure if such a device is possible. > > I think we should have similarly defined value 0 to indicate an unused > lane. None of drivers in mainline uses this line remapping feature, so > changing meaning of the array values wouldn't presumably have any bad > side effects. I'm not sure if it's OK to make a change like this now. > IIUC the MIPI CSI-2 standard requires consecutive data lane indexes, > so valid set of data lanes could be only: <1>, <1, 2>, <1, 2, 3>, > <1, 2, 3, 4>. So there seems to be no issue for MIPI CSI-2. But for > future protocols the current convention might not have been flexible > enough. Given that the video-interfaces binding refers to the clock being on lane 0, I'm not sure it makes sense to reserve this as an unused id -- we'd be saying the lane is the clock to say it's unused, but maybe that doesn't matter. Thanks, Mark. > > > [1] http://www.mipi.org/specifications/camera-interface#CSI2 > > [2] http://www.ti.com/general/docs/lit/getliterature.tsp?literatureNumber=swpu231ao&fileType=pdf > -- > Regards, > Sylwester > -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
