Re: [Qemu-devel] [PATCH] aspeed_scu: Implement RNG register

[Joel Stanley]

On 28 May 2018 at 23:17, Cédric Le Goater <address@hidden> wrote:
> Hello Joel,
>
> On 05/28/2018 02:46 PM, Joel Stanley wrote:
>> The ASPEED SoCs contain a single register that returns random data when
>> read. This models that register so that guests can use it.
>>
>> Signed-off-by: Joel Stanley <address@hidden>
>> ---
>>  hw/misc/aspeed_scu.c | 19 +++++++++++++++++++
>>  1 file changed, 19 insertions(+)
>>
>> diff --git a/hw/misc/aspeed_scu.c b/hw/misc/aspeed_scu.c
>> index 5e6d5744eeca..8fa0cecf0fa1 100644
>> --- a/hw/misc/aspeed_scu.c
>> +++ b/hw/misc/aspeed_scu.c
>> @@ -16,6 +16,7 @@
>>  #include "qapi/visitor.h"
>>  #include "qemu/bitops.h"
>>  #include "qemu/log.h"
>> +#include "crypto/random.h"
>>  #include "trace.h"
>>
>>  #define TO_REG(offset) ((offset) >> 2)
>> @@ -154,6 +155,18 @@ static const uint32_t 
>> ast2500_a1_resets[ASPEED_SCU_NR_REGS] = {
>>       [BMC_DEV_ID]      = 0x00002402U
>>  };
>>
>> +static uint32_t aspeed_scu_get_random(void)
>> +{
>> +    Error *err = NULL;
>> +    uint32_t num;
>> +
>> +    if (qcrypto_random_bytes((uint8_t *)&num, sizeof(num), &err)) {
>> +        error_report_err(err);
>> +    }
>> +
>> +    return num;
>> +}
>> +
>>  static uint64_t aspeed_scu_read(void *opaque, hwaddr offset, unsigned size)
>>  {
>>      AspeedSCUState *s = ASPEED_SCU(opaque);
>> @@ -167,6 +180,9 @@ static uint64_t aspeed_scu_read(void *opaque, hwaddr 
>> offset, unsigned size)
>>      }
>>
>>      switch (reg) {
>> +    case RNG_DATA:
>> +        return aspeed_scu_get_random();
>
> may be we could test bit 1 of RNG_CTRL to check if it is enabled or not.

The RNG is enabled by default, and I didn't find any software that
disables it, but it can't hurt to have that check.

I'll send a v2 with that check.

>
>> +        break;
>>      case WAKEUP_EN:
>>          qemu_log_mask(LOG_GUEST_ERROR,
>>                        "%s: Read of write-only offset 0x%" HWADDR_PRIx "\n",
>> @@ -287,6 +303,9 @@ static void aspeed_scu_realize(DeviceState *dev, Error 
>> **errp)
>>                            TYPE_ASPEED_SCU, SCU_IO_REGION_SIZE);
>>
>>      sysbus_init_mmio(sbd, &s->iomem);
>> +
>> +    if (qcrypto_random_init(errp))
>> +        return;
>>  }
>
> Isn't this routine called from main() already ?

It is indirectly called, yes. I'll remove this.

Cheers,

Joel