On 08/13/2013 10:29 AM, Mark Rutland wrote: > On Tue, Aug 13, 2013 at 04:54:02PM +0100, Stephen Warren wrote: >> On 08/13/2013 03:08 AM, Mark Rutland wrote: >>> On Mon, Aug 12, 2013 at 06:36:30PM +0100, Stephen Warren wrote: >>>> From: Stephen Warren <swarren@xxxxxxxxxx> >>>> >>>> The simplest case of __of_parse_phandle_with_args() implements >>>> of_parse_phandle(), except that it doesn't return the node referenced by >>>> the phandle. Modify it to do so, and then rewrite of_parse_phandle() to >>>> call __of_parse_phandle_with_args() rather than open-coding the simple >>>> case. ... >>> What's the overhead over the old of_parse_phandle? It looks like this is >>> going to do a lot of pointless work beyond what it already does -- >>> parsing each prior entry in the list, and for each prior entry walking >>> the tree in of_find_node_by_phandle. Maybe we don't use long enough >>> phandle lists anywhere for that to be noticeable. >> >> I think the overhead is pretty minimal. The main difference is that the >> new code will loop over the property cell by cell rather than directly >> jump into the required index. That's not likely to be much work for >> typical properties. In particular, no extra DT property lookups are >> performed, since of_parse_phandle() passes in cells_name=NULL, >> cell_count=0, so the cells_name property is not looked up. > > I thought even with your patch we still call of_find_node_by_phandle on > each (phandle) cell as we go over the property, before we hit the check > for cells_name? > > Given that of_find_node_by_phandle does a pretty naive linear search of > the of_allnodes list, that could get significant, especially if all the > elements referred to in the property are near the end of the of_allnodes > list. Oh yes, that is true. I suppose it'd be possible to make the call to of_find_node_by_phandle() conditional; it'd be needed: if (cells_name /* Need to get property from it */ || cur_index == index /* Need to return it */) Do you think it's worth making that change? -- 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
