powerpc/kexec_file: Restore FDT size estimation for kdump kernel

kexec_fdt_totalsize_ppc64() includes the base FDT size in its size
calculation, but commit 3c985d3 ("powerpc: Use common
of_kexec_alloc_and_setup_fdt()") changed the kexec code to use the
generic function of_kexec_alloc_and_setup_fdt() which already includes
the base FDT size. That change made the code overestimate the size a bit
by counting twice the space required for the kernel command line and
/chosen properties.

Therefore change kexec_fdt_totalsize_ppc64() to calculate just the extra
space needed by the kdump kernel, and change the function name so that it
better reflects what the function is now doing.

Signed-off-by: Thiago Jung Bauermann <bauerman@linux.ibm.com>
Reviewed-by: Lakshmi Ramasubramanian <nramas@linux.microsoft.com>
Reviewed-by: Hari Bathini <hbathini@linux.ibm.com>
Acked-by: Michael Ellerman <mpe@ellerman.id.au>
[robh: reword commit msg as no longer a fix from merging to branches]
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210220005204.1417200-1-bauerman@linux.ibm.com

arch/powerpc/include/asm/kexec.h

@@ -124,7 +124,7 @@ int load_crashdump_segments_ppc64(struct kimage *image,
 int setup_purgatory_ppc64(struct kimage *image, const void *slave_code,
 			  const void *fdt, unsigned long kernel_load_addr,
 			  unsigned long fdt_load_addr);
-unsigned int kexec_fdt_totalsize_ppc64(struct kimage *image);
+unsigned int kexec_extra_fdt_size_ppc64(struct kimage *image);
 int setup_new_fdt_ppc64(const struct kimage *image, void *fdt,
 			unsigned long initrd_load_addr,
 			unsigned long initrd_len, const char *cmdline);

arch/powerpc/kexec/elf_64.c

@@ -104,7 +104,7 @@ static void *elf64_load(struct kimage *image, char *kernel_buf,
 
 	fdt = of_kexec_alloc_and_setup_fdt(image, initrd_load_addr,
 					   initrd_len, cmdline,
-					   kexec_fdt_totalsize_ppc64(image));
+					   kexec_extra_fdt_size_ppc64(image));
 	if (!fdt) {
 		pr_err("Error setting up the new device tree.\n");
 		ret = -EINVAL;

arch/powerpc/kexec/file_load_64.c

@@ -927,37 +927,27 @@ int setup_purgatory_ppc64(struct kimage *image, const void *slave_code,
 }
 
 /**
- * kexec_fdt_totalsize_ppc64 - Return the estimated size needed to setup FDT
- *                             for kexec/kdump kernel.
- * @image:                     kexec image being loaded.
+ * kexec_extra_fdt_size_ppc64 - Return the estimated additional size needed to
+ *                              setup FDT for kexec/kdump kernel.
+ * @image:                      kexec image being loaded.
  *
- * Returns the estimated size needed for kexec/kdump kernel FDT.
+ * Returns the estimated extra size needed for kexec/kdump kernel FDT.
  */
-unsigned int kexec_fdt_totalsize_ppc64(struct kimage *image)
+unsigned int kexec_extra_fdt_size_ppc64(struct kimage *image)
 {
-	unsigned int fdt_size;
 	u64 usm_entries;
 
-	/*
-	 * The below estimate more than accounts for a typical kexec case where
-	 * the additional space is to accommodate things like kexec cmdline,
-	 * chosen node with properties for initrd start & end addresses and
-	 * a property to indicate kexec boot..
-	 */
-	fdt_size = fdt_totalsize(initial_boot_params) + (2 * COMMAND_LINE_SIZE);
 	if (image->type != KEXEC_TYPE_CRASH)
-		return fdt_size;
+		return 0;
 
 	/*
-	 * For kdump kernel, also account for linux,usable-memory and
+	 * For kdump kernel, account for linux,usable-memory and
 	 * linux,drconf-usable-memory properties. Get an approximate on the
 	 * number of usable memory entries and use for FDT size estimation.
 	 */
 	usm_entries = ((memblock_end_of_DRAM() / drmem_lmb_size()) +
 		       (2 * (resource_size(&crashk_res) / drmem_lmb_size())));
-	fdt_size += (unsigned int)(usm_entries * sizeof(u64));
-
-	return fdt_size;
+	return (unsigned int)(usm_entries * sizeof(u64));
 }
 
 /**