[RFC v3 PATCH 07/25] ARM: NOMMU: relax restriction on MPU existence

Vladimir Murzin
2016-12-02T15:05:25Z

MPU is must have if we run SMP configurations (since it sets Sharable
attribute), but for UP we can progress further if MPU is not presented.

This patch changes setup_mpu to return error code which we ignore for
boot cpu and only take into account for secondaries.

Cc: Russell King <linux@armlinux.org.uk>
Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>
---
arch/arm/kernel/head-nommu.S | 15 ++++++++++++---
1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/arch/arm/kernel/head-nommu.S b/arch/arm/kernel/head-nommu.S
index 6b4eb27..7317554 100644
--- a/arch/arm/kernel/head-nommu.S
+++ b/arch/arm/kernel/head-nommu.S
@@ -13,6 +13,7 @@
*/
#include <linux/linkage.h>
#include <linux/init.h>
+#include <linux/errno.h>

#include <asm/assembler.h>
#include <asm/ptrace.h>
@@ -112,6 +113,8 @@ ENTRY(secondary_startup)
/* Use MPU region info supplied by __cpu_up */
ldr r6, [r7] @ get secondary_data.mpu_szr
bl __setup_mpu @ Initialize the MPU
+ teq r0, #0
+ bne __error_p
#endif

badr lr, 1f @ return (PIC) address
@@ -201,7 +204,8 @@ ENDPROC(__after_proc_init)
* Region 3: Normal, shared, inaccessible from PL0 to protect the vectors page
*
* r6: Value to be written to DRSR (and IRSR if required) for MPU_RAM_REGION
-*/
+ * r0: non zero value indicates error
+ */

ENTRY(__setup_mpu)

@@ -209,13 +213,13 @@ ENTRY(__setup_mpu)
mrc p15, 0, r0, c0, c1, 4 @ Read ID_MMFR0
and r0, r0, #(MMFR0_PMSA) @ PMSA field
teq r0, #(MMFR0_PMSAv7) @ PMSA v7
- bne __error_p @ Fail: ARM_MPU on NOT v7 PMSA
+ bne __nompu

/* Determine whether the D/I-side memory map is unified. We set the
* flags here and continue to use them for the rest of this function */
mrc p15, 0, r0, c0, c0, 4 @ MPUIR
ands r5, r0, #MPUIR_DREGION_SZMASK @ 0 size d region => No MPU
- beq __error_p @ Fail: ARM_MPU and no MPU
+ beq __nompu
tst r0, #MPUIR_nU @ MPUIR_nU = 0 for unified

/* Setup second region first to free up r6 */
@@ -263,6 +267,11 @@ ENTRY(__setup_mpu)
orr r0, r0, #CR_M @ Set SCTRL.M (MPU on)
mcr p15, 0, r0, c1, c0, 0 @ Enable MPU
isb
+
+ mov r0, #0
+ ret lr
+__nompu:
+ mov r0, #-ENODEV
ret lr
ENDPROC(__setup_mpu)
#endif
--
1.7.9.5