Re: [Qemu-devel] [PATCH v3 6/9] rocker: add new rocker switch device

[Scott Feldman]

On Mon, Jan 12, 2015 at 4:57 AM, Paolo Bonzini <address@hidden> wrote:
>
>
> On 11/01/2015 04:57, address@hidden wrote:
>> +static const MemoryRegionOps rocker_mmio_ops = {
>> +    .read = rocker_mmio_read,
>> +    .write = rocker_mmio_write,
>> +    .endianness = DEVICE_LITTLE_ENDIAN,
>> +    .valid = {
>> +        .min_access_size = 4,
>> +        .max_access_size = 8,
>> +    },
>> +    .impl = {
>> +        .min_access_size = 4,
>> +        .max_access_size = 8,
>> +    },
>> +};
>
> I suggest that you only use 32-bit registers in the internal
> implementation, where writing to the low part of a 64-bit register only
> writes to a latch.  You can then use .impl.max_access_size == 4 but keep
> .valid.max_access_size == 8.
>
> QEMU will then take care of passing 64-bit writes down as two 32-bit
> writes, in increasing address.

I tried setting .impl.max_access_size=4 and the Linux driver self-test
fails on 64-bit reg write/read.  32-bit regs writes/reads are OK.  On
the 64-bit write/read, the self test writes a value and expects to
read back 2x the value written.  After making the change
.impl.max_access_size=4, the reg reads back as 0, regardless of what
was written.

The driver uses writeq/readq for 64-bit writes/reads.

I'm inclined to not change the device and leave .impl.max_access_size=8.

-scott