Re: [PATCH v17 02/10] of: Add a common kexec FDT setup function

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.

<...>

quoted

+
+/*
+ * 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/ (local)

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?

thanks,
  -lakshmi

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