On Thu, Aug 22, 2013 at 04:32:10PM +0100, Sudeep KarkadaNagesha wrote: > On 22/08/13 12:59, Mark Rutland wrote: > > On Wed, Aug 21, 2013 at 11:48:12PM +0100, Stephen Warren wrote: > >> On 08/20/2013 04:00 AM, Sudeep KarkadaNagesha wrote: > >> ... > >>> Until we get more feedback and agreement on new proposal can we have > >>> this simple amendment in this patch to the existing binding ? Since the > >>> new proposal[1] is backward compatible(this patch adding support for > >>> option#5 to existing option#1), we will have to add support for other > >>> binding options in [1] later. > >>> > >>> This is needed to support shared OPPs with simple/single OPP profile > >>> and also to fix the broken and unused binding > >>> @Documentation/devicetree/bindings/cpufreq/arm_big_little_dt.txt > >>> > >>> Regards, > >>> Sudeep > >>> > >>> [1] http://www.spinics.net/lists/cpufreq/msg06563.html > >> > >> Presumably the desire for cpu1's node to say "go look at cpu0's node for > >> OPP" is because they share OPPs. Don't they share OPPs because they are > >> parts of the same device - that device being the CPU complex. As such, > >> why not define the OPPs in /cpus rather than in each of /cpus/cpuN? > > > > I'd very much like for it to be possible to factor out common properties > > into the /cpus node, but it should follow the ePAPR recommendation fo > > being treated as a fallback if not present in a particular /cpus/cpu@N > > node -- that way we can handle clusters with differing OPPs. The > > property might just be a phandle to a table node, but it should be > > possible to make it common. > > > Yes we can have this fallback mechanism, but only from cpu devices(OPP > library handles non-cpu devices too). Ok. > > Referring the table node, I have a generic question on DT nodes. > Does each DT node have to represent a unique device ? If so having a > property common to one/more devices in a separate node doesn't sound > correct. I believe the answer is almost always yes. There are devices with subnodes that represent some logical portion of the device, but I couldn't think of any free-standing nodes that aren't a device or unique firmware interface. > > >> > >> Of course, that doesn't help if there are separate CPU and GPU nodes > >> that just happen to have the same set of OPPs and you want to share them > >> to save DT space. Is that at all likely? > > > > I suspect that the OPPs for CPUs and GPUs are likely to be quite > > distict, and they are logically separate regardless. I'm not averse to > > sharing of tables if we can handle them in a standard fashion. > > > IMO sharing OPPs just for saving DT space might lead to confusions(no > strong opinion though). Agreed. > > >> > >> I'd suggest/bike-shed that operating-points-device is not the correct > >> property name; it somehow implies that the other device actively defines > >> the OPPs for this device, rather than just happening to have the same > >> OPPs. Perhaps "operating-points-identical-to"? > >> > > > > I'd rather not have properties that point elsewhere and say "treat me > > the same as this node". I'd rather we have common properties as > > described above. > > > Agreed, but for platforms with multiple CPU clusters, since we have only > one /cpus node, we ned to have table node which is arguable if node has > represent a device(as mentioned above) I agree that this seems wasteful of space, but I really don't think that pointing at another device you want the OPPs of is the best way of describing the linkage, and I suspect we'll get all sorts of stupid bugs resulting from that style of binding. Consider the following (properties trimmed for brevity): cpus { cpu0: cpu@0 { operating-points-identical-to = <&cpu1>; }; cpu1: cpu@1 { operating-points = <0 100>, <23 47>, <62 970>; } }; If we boot a UP kernel on the above, I assume we won't read the info for cpu1, and thus we won't get operating points info for cpu0. Worse, what if cpu1 has status="disabled"? Does that make its OPP table invalid? What if the bootloader drops cpu1? I really don't like indirecting linkage to a property through an arbitrary node, simply because it happened to have the same property. It creates an artificial depdendency that will lead to problems. Thanks, Mark. -- 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
