On Sun, Jan 05, 2020 at 04:40:58PM +0000, André Przywara wrote: > On 04/01/2020 10:04, Maxime Ripard wrote: > >> But more importantly: what are the guidelines for using this tag? I > >> understand the desire to provide every possible pin description on > >> one hand, but wanting to avoid having *all of them* in *each* .dtb > >> on the other. > > > > Pin groups will take a lot of space in the dtb, and the DT parsing > > will take some measurable time, > > Really? Where is that? In Linux, or in U-Boot, possibly with the caches > off? I am just curious. AFAIK there are some inefficient algorithms in > libfdt (which trade performance for a smaller memory footprint), but I > thought those would be called only very rarely. The last time I measured it was in U-Boot (and for the FIT image, not an actual DT), but the parsing time for a FIT image with a kernel and DTB was around 100ms. (and adding the PSCI and simplefb nodes was in the same order of magnitude). Boot time was very sensitive, and I had to remove both. > >> And should there be a dtc command line option to ignore those tags, > >> or even to apply this tag (virtually) to every node? > > > > Most of the nodes are (reference) leaves in a DT though. Pretty much > > all the device nodes have no references pointing to them, just like > > most of the buses, the CPU nodes, etc. And I'm pretty sure you want to > > keep them :) > > Yeah, that was a New-Year's brain-fart of mine ;-) > > While I was changing the patch I figured that it gets quite lengthy. > Also looking at the a20.dtsi, I see that *all* pin groups have this tag > now. Wouldn't it be easier to introduce *one* tag that applies that to > all children of a node? I don't really know, I'm not sure the proliferation of tags would be a good thing either, and I'm not the dtc maintainer, so I don't really have a say in this :) > Another thing I was wondering about: Would we gain something by not > compiling nodes which have status = "disabled"? This is mentioned as a > generic property in the DT spec, although it says there that the exact > meaning is device dependent. But it sound still worthwhile, especially > since we would avoid more pin groups to be compiled in. I guess that would be good too, but the semantics are a bit different so we'd need a different tag. Maxime
