On Sun, Aug 02, 2015 at 03:27:53PM -0600, Simon Glass wrote:
Hi,
On 27 July 2015 at 11:13, Simon Glass sjg@chromium.org wrote:
Hi,
On 23 July 2015 at 10:51, Stephen Warren swarren@wwwdotorg.org wrote:
From: Thierry Reding treding@nvidia.com
Signed-off-by: Thierry Reding treding@nvidia.com Signed-off-by: Tom Warren twarren@nvidia.com Signed-off-by: Stephen Warren swarren@nvidia.com
Simon,
When Thierry first posted this patch, you responded:
parent = fdt_parent_offset(blob, node);This function is very slow as it must scan the whole tree. Can we instead pass in the parent node?
I don't think that's possible in general. This function is called from fdtdec_get_addr(), and it's easy to find call sites of that function that don't have the parent node available. IIRC, the first couple of example I found scan the DT for a node with a certain compatible value, or look up nodes via aliases, rather than being called while parsing the DT in a top-down tree-like fashion, where the parent node is easily available. I didn't do an exhaustive search after I found a few problematic cases.
Also, how about (in addition) a version of this function that works for devices? Like:
device_get_addr_size(struct udevice *dev, ...)
so that it can handle this for you.
That sounds like a separate patch?
Yes, but I think we should get it in there so that people don't start using this (wildly inefficient) function when they don't need to. I think by passing in the parent node we force people to think about the cost.
Yes the driver model function can be a separate patch, but let's get it in at about the same time. We have dev_get_addr() so could have dev_get_addr_size().
Equally, I see that struct udevice contains an of_offset field, but no parent_of_offset or similar. There is a struct udevice *parent though; is the struct udevice hierarchy guaranteed to 100% match the DT hierarchy? I know this isn't necessarily guaranteed in Linux's device model for example.
Yes it is 100% guaranteed, so dev->parent->of_offset will do the right thing.
As such, this patch seems OK to me as-is.
lib/fdtdec.c | 56 ++++++++++++++++++++++++++++++++++++-------------------- 1 file changed, 36 insertions(+), 20 deletions(-)
This patch has been applied. I'm going to post a revert of this patch. Please can you take a look at the comments above? In particular this function is called from dev_get_addr() which is a core driver model function. It needs to be fast - and in fact dev_get_addr() already has access to the parent node.
Perhaps this could be fixed by doing passing in the parent as an optional argument and then do something like this:
if (parent < 0) { parent = fdt_parent_offset(blob, node); if (parent < 0) { ... } }
In that case callers that have access to the parent node already can pass it in, but others can simply pass in -1 and have the function do the lookup.
Also looking a bit closer this patch does a lot more than 'fix it for 64-bit'. A commit message would be useful to explain what problems it is fixing, etc.
Another point is that fdt_addr_t and fdt_size_t are supposed to match the address size used in the device tree. Is that not the case with Tegra210?
You can't assume that #address-cells and #size-cells will be 2 for all 64-bit platforms. Some may well go with #address-cells = 1 and #size- cells = 1, and I've seen others do #address-cells = 2 and #size-cells = 1. All of these combinations are perfectly valid.
As such, fdt_addr_t and fdt_size_t make sense only if they are the maximum that the architecture can support. Even so an address could technically be larger than that, if it's behind a translated bus, for example.
So what this does is really fix parsing of address and size cells in the general case, though it would still fail for values of #address-cells or #size-cells bigger than 2 (because we don't have a datatype that would be able to contain such large values).
Note that there's also still a corner case that this doesn't handle. The DT specification states, if I remember correctly, that #address-cells and #size-cells are inherited. That means with the current code we will wrongly parse something like this:
/ { ... #address-cells = <1>; #size-cells = <1>; ... bus@XXXXXXXX { ... device@XXXXXXXX { ... reg = <0xXXXXXXXX 0x1000>; ... }; ... }; ... };
According to the DT specification the bus@XXXXXXXX node would inherit #address-cells = <1> and #size-cells = <1> from the root node. However with libfdt what really happens is that since bus@XXXXXXXX does not have either property it will default to 2 in both cases. I'm not sure if this really is a problem. Typically nodes are not nested that deeply, or if they are then, typically, they explicitly contain #address-cells and #size-cells properties.
Thierry