On 10/03/17 09:18, Rob Herring wrote: > For static DT usecases, we don't need the disabled nodes and can skip > unflattening. This saves a significant amount of RAM in memory constrained > cases. In one example on STM32F469, the RAM usage goes from 118K to 26K. > > There are a few cases in the kernel that modify the status property > dynamically. These all are changes from enabled to disabled, depend on > OF_DYNAMIC or are not FDT based (PDT based). > > Cc: Nicolas Pitre <nicolas.pitre@xxxxxxxxxx> > Cc: Frank Rowand <frowand.list@xxxxxxxxx> > Signed-off-by: Rob Herring <robh@xxxxxxxxxx> > --- > For more background, see this presentation from Nico: > > https://connect.linaro.org/resource/sfo17/sfo17-100/ > > drivers/of/fdt.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c > index f8c39705418b..efe91c6856a0 100644 > --- a/drivers/of/fdt.c > +++ b/drivers/of/fdt.c > @@ -396,6 +396,10 @@ static int unflatten_dt_nodes(const void *blob, > if (WARN_ON_ONCE(depth >= FDT_MAX_DEPTH)) > continue; > > + if (!IS_ENABLED(CONFIG_OF_DYNAMIC) && > + !of_fdt_device_is_available(blob, offset)) > + continue; > + > if (!populate_node(blob, offset, &mem, nps[depth], > &nps[depth+1], dryrun)) > return mem - base; > Hi Rob, I strongly support the idea of this patch, but there may be an issue we have to resolve. I'm pretty sure we had talked about the issue a long time ago, and it has been sitting on my todo list. We have two sets of node traversal macros and functions. One set honors the status property, and the other ignores it. If I recall our previous discussion properly, we want the normal usage to honor the status property and only a tiny (or maybe non-existent) set of locations to be allowed to ignore the status property. A rough sense of how often the status property is honored or not is: $ git grep for_each_child_of_node | wc -l 293 $ git grep of_get_next_child | wc -l 103 $ git grep for_each_available_child_of_node | wc -l 106 $ git grep of_get_next_available_child | wc -l 20 Many of the cases where the status flag is ignored will not actually encounter a node that is not available, so many of the cases where status is not checked could currently be checking status. And just for completeness, there are a number of standalone checks for whether a node is available: $ git grep of_device_is_available | wc -l 128 It will be a pain to manually check all of the sites that ignore the status property, but that task should be done. In the mean time, maybe we could flush out the few cases that currently depend on ignoring the status property by - making for_each_child_of_node() and of_get_next_child() actually check for valid status - provide a temporary (one or two kernel release) CONFIG option to allow the old behavior for for_each_child_of_node() and of_get_next_child() just in case we miss any locations that need to be fixed - fix up the few places in core device tree code that actually need to ignore status (if such places exist) In the end, the *_available_*() interfaces should be removed, because the normal behavior of node traversal should be to only traverse nodes that are available. -Frank -- 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
