ARM: zImage: some comments for __armv3_mpu_cache_on

__armv3_mpu_cache_on seems broken.  As there is noone around who knows
about these machines just keep the code as is but point out the strange
things.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

1 files changed, 6 insertions, 0 deletions

diff --git a/arch/arm/boot/compressed/head.S b/arch/arm/boot/compressed/head.S
index 390aa92ef04d..7b7d95c84641 100644
--- a/arch/arm/boot/compressed/head.S
+++ b/arch/arm/boot/compressed/head.S
@@ -396,12 +396,18 @@ __armv3_mpu_cache_on:
 
                 mov     r0, #0
                 mcr     p15, 0, r0, c7, c0, 0   @ invalidate whole cache v3
+                /*
+                 * ?? ARMv3 MMU does not allow reading the control register,
+                 * does this really work on ARMv3 MPU?
+                 */
                 mrc     p15, 0, r0, c1, c0, 0   @ read control reg
                                                 @ .... .... .... WC.M
                 orr     r0, r0, #0x000d         @ .... .... .... 11.1
+                /* ?? this overwrites the value constructed above? */
                 mov     r0, #0
                 mcr     p15, 0, r0, c1, c0, 0   @ write control reg
 
+                /* ?? invalidate for the second time? */
                 mcr     p15, 0, r0, c7, c0, 0   @ invalidate whole cache v3
                 mov     pc, lr