[PATCH v3 1/4] hw/intc/armv7m_nvic: Correct handling of CCR.BFHFNMIGN

[Peter Maydell <peter.maydell@linaro.org>]

The CCR is a register most of whose bits are banked between security
states but where BFHFNMIGN is not, and we keep it in the non-secure
entry of the v7m.ccr[] array.  The logic which tries to handle this
bit fails to implement the "RAZ/WI from Nonsecure if AIRCR.BFHFNMINS
is zero" requirement; correct the omission.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
Changes since v2: get the "WI" bit right
---
 hw/intc/armv7m_nvic.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/hw/intc/armv7m_nvic.c b/hw/intc/armv7m_nvic.c
index f63aa2d8713..0d8426dafc9 100644
--- a/hw/intc/armv7m_nvic.c
+++ b/hw/intc/armv7m_nvic.c
@@ -1106,6 +1106,12 @@ static uint32_t nvic_readl(NVICState *s, uint32_t offset, MemTxAttrs attrs)
          */
         val = cpu->env.v7m.ccr[attrs.secure];
         val |= cpu->env.v7m.ccr[M_REG_NS] & R_V7M_CCR_BFHFNMIGN_MASK;
+        /* BFHFNMIGN is RAZ/WI from NS if AIRCR.BFHFNMINS is 0 */
+        if (!attrs.secure) {
+            if (!(cpu->env.v7m.aircr & R_V7M_AIRCR_BFHFNMINS_MASK)) {
+                val &= ~R_V7M_CCR_BFHFNMIGN_MASK;
+            }
+        }
         return val;
     case 0xd24: /* System Handler Control and State (SHCSR) */
         if (!arm_feature(&cpu->env, ARM_FEATURE_V7)) {
@@ -1683,6 +1689,15 @@ static void nvic_writel(NVICState *s, uint32_t offset, uint32_t value,
                 (cpu->env.v7m.ccr[M_REG_NS] & ~R_V7M_CCR_BFHFNMIGN_MASK)
                 | (value & R_V7M_CCR_BFHFNMIGN_MASK);
             value &= ~R_V7M_CCR_BFHFNMIGN_MASK;
+        } else {
+            /*
+             * BFHFNMIGN is RAZ/WI from NS if AIRCR.BFHFNMINS is 0, so
+             * preserve the state currently in the NS element of the array
+             */
+            if (!(cpu->env.v7m.aircr & R_V7M_AIRCR_BFHFNMINS_MASK)) {
+                value &= ~R_V7M_CCR_BFHFNMIGN_MASK;
+                value |= cpu->env.v7m.ccr[M_REG_NS] & R_V7M_CCR_BFHFNMIGN_MASK;
+            }
         }
 
         cpu->env.v7m.ccr[attrs.secure] = value;
-- 
2.20.1