[U-Boot] [PATCH] fdt: Try to read #address-cells/size-cells from parent
David Gibson
david at gibson.dropbear.id.au
Wed Mar 16 23:47:27 CET 2016
On Wed, Mar 16, 2016 at 05:18:25PM +0100, Michal Simek wrote:
> Hi David,
>
> On 15.3.2016 01:27, David Gibson wrote:
> > On Mon, Mar 14, 2016 at 10:10:58PM +0100, Michal Simek wrote:
> >> On 13.3.2016 02:54, Simon Glass wrote:
> >>> Hi Michal,
> >>>
> >>> On 16 February 2016 at 09:10, Michal Simek <michal.simek at xilinx.com> wrote:
> >>>> Hi Simon,
> >>>>
> >>>> On 16.2.2016 17:00, Simon Glass wrote:
> >>>>> Hi Michal,
> >>>>>
> >>>>> On 15 February 2016 at 02:58, Michal Simek <michal.simek at xilinx.com> wrote:
> >>>>>> Hi Simon,
> >>>>>>
> >>>>>> On 10.2.2016 13:04, Michal Simek wrote:
> >>>>>>> Read #address-cells and #size-cells from parent if they are not present in
> >>>>>>> current node.
> >>>>>>>
> >>>>>>> Signed-off-by: Michal Simek <michal.simek at xilinx.com>
> >>>>>>> ---
> >>>>>>>
> >>>>>>> I have code which read information about memory for zynqmp but memory
> >>>>>>> node most of the time doesn't contain #address/size-cells which are
> >>>>>>> present in parent node.
> >>>>>>> That's why let's try to read it from parent.
> >>>>>>>
> >>>>>>> Also I think that we shouldn't return 2 if property is not found because
> >>>>>>> it has side effect on 32bit systems with #address/size-cells = <1>;
> >>>>>>>
> >>>>>>> ---
> >>>>>>> lib/libfdt/fdt_addresses.c | 18 ++++++++++++++----
> >>>>>>> 1 file changed, 14 insertions(+), 4 deletions(-)
> >>>>>>>
> >>>>>>> diff --git a/lib/libfdt/fdt_addresses.c b/lib/libfdt/fdt_addresses.c
> >>>>>>> index 76054d98e5fd..b164d0988079 100644
> >>>>>>> --- a/lib/libfdt/fdt_addresses.c
> >>>>>>> +++ b/lib/libfdt/fdt_addresses.c
> >>>>>>> @@ -19,10 +19,15 @@ int fdt_address_cells(const void *fdt, int nodeoffset)
> >>>>>>> const fdt32_t *ac;
> >>>>>>> int val;
> >>>>>>> int len;
> >>>>>>> + int parent;
> >>>>>>>
> >>>>>>> ac = fdt_getprop(fdt, nodeoffset, "#address-cells", &len);
> >>>>>>> - if (!ac)
> >>>>>>> - return 2;
> >>>>>>> + if (!ac) {
> >>>>>>> + parent = fdt_parent_offset(fdt, nodeoffset);
> >>>>>>> + ac = fdt_getprop(fdt, parent, "#address-cells", &len);
> >>>>>>> + if (!ac)
> >>>>>>> + return 2;
> >>>>>>> + }
> >>>>>>>
> >>>>>>> if (len != sizeof(*ac))
> >>>>>>> return -FDT_ERR_BADNCELLS;
> >>>>>>> @@ -39,10 +44,15 @@ int fdt_size_cells(const void *fdt, int nodeoffset)
> >>>>>>> const fdt32_t *sc;
> >>>>>>> int val;
> >>>>>>> int len;
> >>>>>>> + int parent;
> >>>>>>>
> >>>>>>> sc = fdt_getprop(fdt, nodeoffset, "#size-cells", &len);
> >>>>>>> - if (!sc)
> >>>>>>> - return 2;
> >>>>>>> + if (!sc) {
> >>>>>>> + parent = fdt_parent_offset(fdt, nodeoffset);
> >>>>>>> + sc = fdt_getprop(fdt, parent, "#size-cells", &len);
> >>>>>>> + if (!sc)
> >>>>>>> + return 2;
> >>>>>>> + }
> >>>>>>>
> >>>>>>> if (len != sizeof(*sc))
> >>>>>>> return -FDT_ERR_BADNCELLS;
> >>>>>>>
> >>>>>>
> >>>>>> Simon: Any comment?
> >>>>>
> >>>>> It seems risky to change the behaviour here. Also fdt_parent_offset() is slow.
> >>>>>
> >>>>> Can you point me to the binding / example DT that you are trying to parse?
> >>>>
> >>>> Look at dram_init(), etc.
> >>>> https://github.com/Xilinx/u-boot-xlnx/blob/master/board/xilinx/zynqmp/zynqmp.c
> >>>>
> >>>> fdt_get_reg() is calling fdt_size_cells()
> >>>>
> >>>>
> >>>> And this is DTS fragment.
> >>>> #address-cells = <2>;
> >>>> #size-cells = <1>;
> >>>>
> >>>> memory {
> >>>> device_type = "memory";
> >>>> reg = <0x0 0x0 0x80000000>, <0x8 0x00000000 0x80000000>;
> >>>> };
> >>>>
> >>>> Code is in memory node I need to work with and asking for size-cells.
> >>>> Current code returns 2 instead of error and the rest of code just works
> >>>> with size = 2 which is incorrect for this setup.
> >>>>
> >>>> I have already changed size-cells = 2 in our repo because I need to
> >>>> support for more than 4GB memory anyway but this should point to the
> >>>> problem in that generic functions.
> >>>
> >>> I think this should go in a higher-level function. I very much doubt
> >>> that this patch would be accepted upstream.
> >>>
> >>> Can you find the caller and make it call this function again (for the
> >>> parent) when no nothing is found on the first call? Hopefully this
> >>> caller will have access to the parent node and will not need to call
> >>> fdt_parent_offset().
> >>
> >> The funny part is that nothing is found means return 2. If this returns
> >> something <0 then there is not a problem to try it with parents.
> >
> > I don't have the full context of this thread, so it's a bit hard to be
> > sure, but this doesn't look right from what I can see. Two things to
> > remember here:
> >
> > * #address-cells and #size-cells describe the format of addresses
> > for children of this node, not this node itself. So if you're
> > looking to parse 'reg' for this node, you *always* need to look at
> > the parent, not just as a fallback.
>
> ok that means that I should fix my code to find parent of current node
> and then read address and size cells.
>
> fdt - actual memory node
> parent = fdt_parent_offset(fdt, nodeoffset);
> address_cells = fdt_address_cells(parent, nodeoffset);
> size_cells = fdt_size_cells(parent, nodeoffset);
That's correct. One way to look at it that #address-cells and
#size-cells are properties of the bus anchored at this node, rather
than properties of the node itself.
> > * #address-cells and #size-cells are *not* inherited. If they're
> > missing in a node, then the format for its children's addresses is
> > 2 cell addresses and 2 cell sizes, it is *not* correct to look at
> > the next parent up for these properties.
> >
>
> ok. And I expect that this is in spec.
Yes. Actually relying on the default values is discouraged, of
course: you should include #address-cells and #size-cells for any node
with children.
> Definitely thank you for your input it was very helpful.
>
> Thanks,
> Michal
>
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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