Re: [Qemu-devel] [PATCH v2 1/9] arm: add missing scu registers

[Peter Maydell]

On 22 December 2011 18:20, Mark Langsdorf <address@hidden> wrote:
> From: Rob Herring <address@hidden>
>
> Add power control and non-secure access ctrl registers

Commit message says it's adding the non-secure
access control register, but the patch is only
doing power control.

>
> Signed-off-by: Rob Herring <address@hidden>
> Signed-off-by: Mark Langsdorf <address@hidden>
> ---
> Changes from v1:
>        Added VMState support
>        Checked alignment of writes to the power control register
>
>  hw/a9mpcore.c |   34 ++++++++++++++++++++++++++++++++--
>  1 files changed, 32 insertions(+), 2 deletions(-)
>
> diff --git a/hw/a9mpcore.c b/hw/a9mpcore.c
> index cd2985f..875ae98 100644
> --- a/hw/a9mpcore.c
> +++ b/hw/a9mpcore.c
> @@ -29,6 +29,7 @@ gic_get_current_cpu(void)
>  typedef struct a9mp_priv_state {
>     gic_state gic;
>     uint32_t scu_control;
> +    uint32_t scu_status;
>     uint32_t old_timer_status[8];
>     uint32_t num_cpu;
>     qemu_irq *timer_irq;
> @@ -48,7 +49,13 @@ static uint64_t a9_scu_read(void *opaque, 
> target_phys_addr_t offset,
>     case 0x04: /* Configuration */
>         return (((1 << s->num_cpu) - 1) << 4) | (s->num_cpu - 1);
>     case 0x08: /* CPU Power Status */
> -        return 0;
> +        return s->scu_status;
> +    case 0x09: /* CPU status.  */
> +        return s->scu_status >> 8;
> +    case 0x0a: /* CPU status.  */
> +        return s->scu_status >> 16;
> +    case 0x0b: /* CPU status.  */
> +        return s->scu_status >> 24;
>     case 0x0c: /* Invalidate All Registers In Secure State */
>         return 0;
>     case 0x40: /* Filtering Start Address Register */
> @@ -73,6 +80,29 @@ static void a9_scu_write(void *opaque, target_phys_addr_t 
> offset,
>         break;
>     case 0x4: /* Configuration: RO */
>         break;
> +    case 0x08: /* Power Control  */
> +        s->scu_status = value;
> +        break;

This does the wrong thing for a byte or halfword
write to 0x8. (Byte writes in particular are going to be the
common case for this register for obvious reasons.)

> +    case 0x09: /* Power Control  */
> +        s->scu_status &= ~(0xff << 8);
> +        s->scu_status |= (value & 0xff) << 8;
> +        break;
> +    case 0x0A: /* Power Control  */
> +        if (size == 1) {
> +            s->scu_status &= ~(0xff << 16);
> +            s->scu_status |= (value & 0xff) << 16;
> +        } else if (size == 2) {
> +            s->scu_status &= ~(0xffff << 16);
> +            s->scu_status |= (value & 0xffff) << 16;
> +        } else {
> +            /* illegal number of bytes */
> +            break;
> +        }
> +        break;
> +    case 0x0B: /* Power Control  */
> +        s->scu_status &= ~(0xff << 24);
> +        s->scu_status |= (value & 0xff) << 24;
> +        break;

How about:
 switch (size) {
     case 1:
        mask = 0xff;
        break;
     case 2:
        mask = 0xffff;
        break;
     case 4:
        mask = 0xffffffff;
        break;
 }

Then the register write code simplifies to:
   case 0x08: case 0x09: case 0xa: case 0xb:
      shift = (offset - 0x8) * 8;
      s->scu_status &= ~(mask << shift);
      s->scu_status |= ((value & mask) << shift);
      break;

(written on the hoof and untested!)

>     case 0x0c: /* Invalidate All Registers In Secure State */
>         /* no-op as we do not implement caches */
>         break;
> @@ -80,7 +110,6 @@ static void a9_scu_write(void *opaque, target_phys_addr_t 
> offset,
>     case 0x44: /* Filtering End Address Register */
>         /* RAZ/WI, like an implementation with only one AXI master */
>         break;
> -    case 0x8: /* CPU Power Status */
>     case 0x50: /* SCU Access Control Register */
>     case 0x54: /* SCU Non-secure Access Control Register */
>         /* unimplemented, fall through */
> @@ -173,6 +202,7 @@ static const VMStateDescription vmstate_a9mp_priv = {
>     .minimum_version_id = 1,
>     .fields = (VMStateField[]) {
>         VMSTATE_UINT32(scu_control, a9mp_priv_state),
> +        VMSTATE_UINT32(scu_status, a9mp_priv_state),
>         VMSTATE_UINT32_ARRAY(old_timer_status, a9mp_priv_state, 8),
>         VMSTATE_END_OF_LIST()
>     }

This breaks migration compatibility. You want:
 * set .version_id to 2
 * leave .minimum_version_id as 1
 * the new field should go at the end of the list and be:
 VMSTATE_UINT32_V(scu_status, a9mp_priv_state, 2),
(which says it only exists in version 2).

-- PMM