On Sun, Oct 8, 2017 at 5:57 PM, Frank Rowand <frowand.list@xxxxxxxxx> wrote: > 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. Ignoring status is a bug for a static DT. There could be places that expect the node to be present, but disabled. Those may be bugs too. > 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. For many nodes, status simply makes no sense or at least is undefined. > 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 I'm surprised it's that many. It's a low-level detail that the core should handle. We'd also need to make things like of_find_node_by_name honor status. > 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. I'm not sure this is really something we want or need to fix. I could just make this depend on OF_KOBJ instead. Then practically no one would see any change as almost everyone enables sysfs (and in turn /proc/device-tree). Rob -- 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
