Messages in this thread | | | Subject | Re: [PATCH v17 02/10] of: Add a common kexec FDT setup function | From | Lakshmi Ramasubramanian <> | Date | Fri, 12 Feb 2021 09:19:00 -0800 |
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On 2/12/21 6:38 AM, Rob Herring wrote: > On Thu, Feb 11, 2021 at 7:17 PM Lakshmi Ramasubramanian > <nramas@linux.microsoft.com> wrote: >> >> On 2/11/21 5:09 PM, Thiago Jung Bauermann wrote: >>> >>> There's actually a complication that I just noticed and needs to be >>> addressed. More below. >>> >> >> <...> >> >>>> + >>>> +/* >>>> + * of_kexec_alloc_and_setup_fdt - Alloc and setup a new Flattened Device Tree >>>> + * >>>> + * @image: kexec image being loaded. >>>> + * @initrd_load_addr: Address where the next initrd will be loaded. >>>> + * @initrd_len: Size of the next initrd, or 0 if there will be none. >>>> + * @cmdline: Command line for the next kernel, or NULL if there will >>>> + * be none. >>>> + * >>>> + * Return: fdt on success, or NULL errno on error. >>>> + */ >>>> +void *of_kexec_alloc_and_setup_fdt(const struct kimage *image, >>>> + unsigned long initrd_load_addr, >>>> + unsigned long initrd_len, >>>> + const char *cmdline) >>>> +{ >>>> + void *fdt; >>>> + int ret, chosen_node; >>>> + const void *prop; >>>> + unsigned long fdt_size; >>>> + >>>> + fdt_size = fdt_totalsize(initial_boot_params) + >>>> + (cmdline ? strlen(cmdline) : 0) + >>>> + FDT_EXTRA_SPACE; >>> >>> Just adding 4 KB to initial_boot_params won't be enough for crash >>> kernels on ppc64. The current powerpc code doubles the size of >>> initial_boot_params (which is normally larger than 4 KB) and even that >>> isn't enough. A patch was added to powerpc/next today which uses a more >>> precise (but arch-specific) formula: >>> >>> https://lore.kernel.org/linuxppc-dev/161243826811.119001.14083048209224609814.stgit@hbathini/ >>> >>> So I believe we need a hook here where architectures can provide their >>> own specific calculation for the size of the fdt. Perhaps a weakly >>> defined function providing a default implementation which an >>> arch-specific file can override (a la arch_kexec_kernel_image_load())? >>> >>> Then the powerpc specific hook would be the kexec_fdt_totalsize_ppc64() >>> function from the patch I linked above. >>> >> >> Do you think it'd better to add "fdt_size" parameter to >> of_kexec_alloc_and_setup_fdt() so that the caller can provide the >> desired FDT buffer size? > > Yes, I guess so. But please define the param as extra size, not total > size. The kernel command line size addition can be in the common code.
Will do. Just to clarify -
The common code will do:
fdt_totalsize(initial_boot_params) + strlen(cmdline) + extra_fdt_size
The caller will pass "extra_fdt_size" ARM64 => 4KB PPC64 => fdt_totalsize(initial_boot_params) - which will be updated when the patch Thiago had referred to is merged.
> > The above change is also going to conflict, so I think this may have > to wait. Or I'll take the common and arm bits and powerpc can be > converted next cycle (or after the merge window). >
thanks.
-lakshmi
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