Hi Robert,
On 19 May 2016 at 06:51, Robert P. J. Day <rpj...@crashcourse.ca> wrote:
>
> curious about recommended coding style related to modifying and
> verifying FDTs ... i'm perusing common/image-fdt.c and can see the
> order of (possible) operations here in the function
> image_setup_libfdt():
>
> * arch_fixup_fdt()
> * ft_board_setup()
> * ft_system_setup()
> * fdt_fixup_ethernet()
> ... etc etc ...
> * ft_verify_fdt()
>
> where an earlier comment explains that last routine:
>
> /*
> * Verify the device tree.
> *
> * This function is called after all device tree fix-ups have been enacted,
> * so that the final device tree can be verified. The definition of
> "verified"
> * is up to the specific implementation. However, it generally means that the
> * addresses of some of the devices in the device tree are compared with the
> * actual addresses at which U-Boot has placed them.
> *
> * Returns 1 on success, 0 on failure. If 0 is returned, U-Boot will halt the
> * boot process.
> */
> __weak int ft_verify_fdt(void *fdt)
> {
> return 1;
> }
>
>
> which seems reasonable ... after you've mangled your FDT in every
> way you need, optionally supply a routine to make sure it looks sane.
>
> however, for the freescale board mpc8641hpcn.c, here's part of the
> ft_board_setup() routine (actually, this is pretty much all that
> function does):
>
>
> if (tmp) {
> u64 addr;
>
> if (addrcells == 1)
> addr = *(u32 *)tmp;
> else
> addr = *tmp;
>
> if (addr != CONFIG_SYS_CCSRBAR_PHYS)
> printf("WARNING: The CCSRBAR address in your .dts "
> "does not match the address of the CCSR "
> "in u-boot. This means your .dts might "
> "be old.\n");
> }
>
> so the board setup routine is doing some quick sanity checking, which
> is perfectly fine, but seems to be exactly the sort of thing
> ft_verify_fdt() was designed for.
>
> obviously, one can add sanity checking to any of those routines
> depending on how early you want to notice stuff -- is there somewhere
> a style guide that gives recommendations? just looking for "best
> practices," thanks.
>
> i'm sure there will be more FDT-related questions coming ... thank
> you for your patience.
My suggestion would be to always use an 'fdt_' prefix.
Regards,
Simon
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