Re: [Qemu-devel] [PATCH] s390x: initialize virtio dev region

[Alexander Graf <agraf@suse.de>]

On 11/11/2011 05:11 PM, Peter Maydell wrote:
> On 11 November 2011 15:59, Alexander Graf<agraf@suse.de>  wrote:
>> This is the machine init function. The s390 virtio machine's ram layout is
>> defined to be exactly as I posted in the previous post. So there won't be
>> any ram starts at != 0 or multiple mappings :).
> That's the layout of the RAM in target_phys_addr_t space.
> The layout of the ram in ram_addr_t space is not guaranteed
> to be the same, it just happens to be in this case.
>
>>>> On 10.11.2011, at 02:36, Peter Maydell wrote:
>>> In summary, either:
>>> (1) you need to ask the memory region for its ram_addr_t
>>> [there doesn't seem to be an API for this at the moment],
>>> do arithmetic on ram_addr_t's and use qemu_get_ram_ptr() to
>>> get a host pointer corresponding to that ram_addr_t
>>> or (2) you need to do your arithmetic in target_phys_addr_t's
>>> (and then you can say your RAM starts at physaddr 0, which
>>> is guaranteed, rather than at ram_addr_t 0, which isn't)
>>> and use cpu_physical_memory_map/unmap().
>> I still don't get it. What I want is:
>>
>>   for (i = ram_size; i<  my_ram_size; i++)
>>     stb_phys(env, i, 0);
>>
>> cpu_physical_memory_map gives me a pointer to the memory region between
>> ram_size and my_ram_size. I memset(0) it. I don't see how I could possibly
>> have different offsets anywhere. If cpu_physical_memory_map would take
>> anything different than physical address, a lot of assumptions in QEMU code
>> would break.
> Yes, so that's option (2) and you need to be using a target_phys_addr_t.

But ram_size is ram_addr_t and is the ram size that I have available to 
use, so it's exactly the address that I want. I don't see your point. 
Should go jump through random useless hoops of doing

   target_phys_addr_t ram_end = ram_size;

just because there are some subtile semantic differences between the two 
variables? They're integers at the end of the day. Both of them.


Alex