On Wed, Nov 09, 2016 at 10:58:32AM -0600, Benjamin Fair wrote: > This patch extends the capability of libfdt to parse the contents of device > trees in a similar manner to fdt_address_cells and fdt_size_cells. > > It adds a helper function which reads the address and size of a device from > the reg property and performs basic sanity checks. > > It does not perform translation to a physical address using the ranges > properties of parents, but this enhancement may be added as a separate > function in the future. I like the concept of a helper to read entries from reg, but there some things about the execution of it I think need some more thought. > Signed-off-by: Benjamin Fair <b-fair@xxxxxx> > --- > > The intent of this patch is similar to the commit "libfdt: Add helpers to read > #address-cells and #size-cells" [1]. > > It is related to "libfdt: add address translation support" [2] but does not > attempt to perform address translation and was written from scratch rather than > reusing GPL code. If the issues with that patch are resolved, that > functionality will complement what is added in this patch. > > [1] http://www.spinics.net/lists/devicetree-compiler/msg00113.html > [2] http://www.spinics.net/lists/devicetree-compiler/msg00093.html > > libfdt/fdt_addresses.c | 62 ++++++++++++++++++++++++++++++++++++++++++ > libfdt/libfdt.h | 29 ++++++++++++++++++++ > libfdt/version.lds | 1 + > tests/.gitignore | 1 + > tests/Makefile.tests | 2 +- > tests/addr_size.c | 74 ++++++++++++++++++++++++++++++++++++++++++++++++++ > tests/addresses.dts | 11 ++++++++ > tests/run_tests.sh | 1 + > 8 files changed, 180 insertions(+), 1 deletion(-) > create mode 100644 tests/addr_size.c > > diff --git a/libfdt/fdt_addresses.c b/libfdt/fdt_addresses.c > index eff4dbc..92cbed9 100644 > --- a/libfdt/fdt_addresses.c > +++ b/libfdt/fdt_addresses.c > @@ -55,6 +55,9 @@ > > #include "libfdt_internal.h" > > +#define BYTES_PER_CELL 4 > +#define BITS_PER_CELL 32 You shouldn't need these. BYTES_PER_CELL == sizeof(fdt32_t). > + > int fdt_address_cells(const void *fdt, int nodeoffset) > { > const fdt32_t *ac; > @@ -94,3 +97,62 @@ int fdt_size_cells(const void *fdt, int nodeoffset) > > return val; > } > + > +static uint64_t _fdt_read_cells(const fdt32_t *cells, int n) This is a reasonable helper, but the name is bad. "read_cells" suggests it can read some arbitrary number of cells, but in fact all it can do is read a 32-bit int or a 64-bit int. Plus everything is made up of cells, but more specifically what you're doing here is interpreting several cells as an integer in the usual encoding. > +{ > + int i; > + uint64_t res; > + > + /* TODO: Support values larger than 2 cells */ I don't really see any way you could support >2 cells without completely changing the interface. > + if (n > 2) > + return -FDT_ERR_BADNCELLS; > + > + res = 0; > + for (i = 0; i < n; i++) { > + res <<= BITS_PER_CELL; > + res |= fdt32_to_cpu(cells[i]); > + } > + > + return res; > +} > + > +int fdt_simple_addr_size(const void *fdt, int nodeoffset, int idx, > + uintptr_t *addr, size_t *size) > +{ > + int parent; > + int ac, sc, reg_stride; > + int res; > + const fdt32_t *reg; > + > + reg = fdt_getprop(fdt, nodeoffset, "reg", &res); > + if (res < 0) > + return res; > + > + parent = fdt_parent_offset(fdt, nodeoffset); > + if (parent < 0) > + return res; So, fdt_parent_offset() is very expensive, I wouldn't recommend it in a function that's likely to be called a lot like this. Instead I'd suggest a function which takes the parent offset as a parameter, and optionally a wrapper that uses fdt_parent_offset(). > + > + ac = fdt_address_cells(fdt, parent); > + if (ac < 0) > + return ac; > + > + sc = fdt_size_cells(fdt, parent); > + if (sc < 0) > + return sc; > + > + reg_stride = ac + sc; > + /* > + * res is the number of bytes read and must be an even multiple of the > + * sum of ac and sc. > + */ > + if ((res % (reg_stride * BYTES_PER_CELL)) != 0) > + return -FDT_ERR_BADVALUE; > + > + if (addr) > + *addr = (uintptr_t) _fdt_read_cells(®[reg_stride * idx], ac); I don't think uintptr_t makes sense here. The addresses in the device tree are in whatever bus they're in, and there are a whole stack of reasons that could be unrelated to the pointer size of environment libfdt is running in: - The device may be on a subordinate bus whose addresses need to be translated - Even at the top-level, the reg properties represent *physical* addresses, which may not be the same as virtual addresses in code running on the system - libfdt may be running on a completely different system from the one the device tree in question is aimed at (bootloaders are only one use case for libfdt). > + if (size) > + *size = (size_t) _fdt_read_cells(®[ac + reg_stride * idx], > + sc); Likewise size_t isn't necessarily right here, although I suspect it's less likely to break in practice. > + return 0; > +} -- 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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