On 10/09/17 11:59, Rob Herring wrote: > 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). Yes, depending on OF_KOBJ should reduce the risk significantly. Good enough for me (you can take my reviewed-by for that). I'm still leaving a clean up of checking or ignoring status on my long term todo list. -Frank > > 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
