[POWERPC] Fix crashkernel= handling when no crashkernel= specified

Commit edd8ce67436851a62f99f1d9707b40ea6a8e5323 (Use extended crashkernel
command line on ppc64), changed the logic in reserve_crashkernel()
which deals with the crashkernel= command line option.

This introduced a bug in the case when there is no crashkernel= option,
or it is incorrect.  We would fall through and calculate the crash_size
based on the existing values in crashk_res.  If both start and end are 0,
the default, we calculate the crash_size as 1 byte - which is wrong.

Rework the logic so that we use crashk_res, regardless of whether it's
set by the command line or via the device tree (see prom.c).  Then check
if we have an empty range (end == start), and if so make sure to set
both end and start to zero (this is checked in machine_kexec_64.c).  Then
we calculate the crash_size once we know we have a non-zero range.

Finally we always want to warn the user if they specify a base != 32MB,
so remove the special case for that in the command line parsing case.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>

1 files changed, 6 insertions, 6 deletions

diff --git a/arch/powerpc/kernel/machine_kexec.c b/arch/powerpc/kernel/machine_kexec.c
index 2d202f274e73..29a0e039d436 100644
--- a/arch/powerpc/kernel/machine_kexec.c
+++ b/arch/powerpc/kernel/machine_kexec.c
@@ -74,20 +74,20 @@ void __init reserve_crashkernel(void)
         ret = parse_crashkernel(boot_command_line, lmb_phys_mem_size(),
                         &crash_size, &crash_base);
         if (ret == 0 && crash_size > 0) {
-                if (crash_base == 0)
-                        crash_base = KDUMP_KERNELBASE;
                 crashk_res.start = crash_base;
-        } else {
-                /* handle the device tree */
-                crash_size = crashk_res.end - crashk_res.start + 1;
+                crashk_res.end = crash_base + crash_size - 1;
         }
 
-        if (crash_size == 0)
+        if (crashk_res.end == crashk_res.start) {
+                crashk_res.start = crashk_res.end = 0;
                 return;
+        }
 
         /* We might have got these values via the command line or the
          * device tree, either way sanitise them now. */
 
+        crash_size = crashk_res.end - crashk_res.start + 1;
+
         if (crashk_res.start != KDUMP_KERNELBASE)
                 printk("Crash kernel location must be 0x%x\n",
                                 KDUMP_KERNELBASE);