[Xen-changelog] [xen staging] xen/arm32: head: Rework and document check_cpu_mode()

[patchbot@xxxxxxx]

commit 1145ea989613f448e401caf004d2de26d834a267
Author:     Julien Grall <julien.grall@xxxxxxx>
AuthorDate: Tue Apr 16 14:53:19 2019 +0100
Commit:     Julien Grall <julien.grall@xxxxxxx>
CommitDate: Sat Sep 7 12:10:38 2019 +0100

    xen/arm32: head: Rework and document check_cpu_mode()
    
    A branch in the success case can be avoided by inverting the branch
    condition. At the same time, remove a pointless comment as Xen can only
    run at Hypervisor Mode.
    
    Lastly, document the behavior and the main registers usage within the
    function.
    
    Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
    Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
---
 xen/arch/arm/arm32/head.S | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/xen/arch/arm/arm32/head.S b/xen/arch/arm/arm32/head.S
index 4285f76463..c7b4fe4cd4 100644
--- a/xen/arch/arm/arm32/head.S
+++ b/xen/arch/arm/arm32/head.S
@@ -206,6 +206,16 @@ secondary_switched:
         b     launch
 ENDPROC(init_secondary)
 
+/*
+ * Check if the CPU supports virtualization extensions and has been booted
+ * in Hypervisor mode.
+ *
+ * This function will never return when the CPU doesn't support
+ * virtualization extensions or is booted in another mode than
+ * Hypervisor mode.
+ *
+ * Clobbers r0 - r3
+ */
 check_cpu_mode:
         /* Check that this CPU has Hyp mode */
         mrc   CP32(r0, ID_PFR1)
@@ -220,15 +230,12 @@ check_cpu_mode:
         mrs   r0, cpsr
         and   r0, r0, #0x1f          /* Mode is in the low 5 bits of CPSR */
         teq   r0, #0x1a              /* Hyp Mode? */
-        beq   hyp
+        moveq pc, lr                 /* Yes, return */
 
         /* OK, we're boned. */
         PRINT("- Xen must be entered in NS Hyp mode -\r\n")
         PRINT("- Please update the bootloader -\r\n")
         b     fail
-
-hyp:    PRINT("- Xen starting in Hyp mode -\r\n")
-        mov   pc, lr
 ENDPROC(check_cpu_mode)
 
 zero_bss:
--
generated by git-patchbot for /home/xen/git/xen.git#staging

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