Re: [Qemu-devel] [PATCHv4 09/13] lance: move TYPE_LANCE and SysBusPCNetState from lance.c to lance.h

[Mark Cave-Ayland]

On 30/10/17 18:45, Philippe Mathieu-Daudé wrote:

>>>>>>> +/*
>>>>>>> + * QEMU AMD PC-Net II (Am79C970A) emulation
>>>>>>
>>>>>> Filename says this is Lance ethernet, but the comment says it's PC-Net ?
>>>>>
>>>>> According to the datasheet for Am79C970A, the original Lance is an
>>>>> Am7990 device and the Am79C970A aka PCNet-PCI II as emulated by QEMU is
>>>>> register-compatible with it.
>>>>>
>>>>> I guess the comment above is more technically correct, but I'm happy to
>>>>> adjust it in my local tree if you still feel it needs to change?
>>>
>>> I think we should have a comment that says what the file is
>>> for. Since this is a different file from pcnet.h, we should
>>> have a comment that isn't the same as the pcnet.h one.
>>> I don't particularly mind what it says, as long as it briefly
>>> explains what's in the file (and by implication what distinguishes
>>> things in this file from things in the other).
>>
>> Okay then how about something along the lines of:
>>
>>  * QEMU Lance (Am7990) device emulation
>>  *
>>  * Copyright (c) 2004 Antony T Curtis
>>  * Copyright (c) 2017 Mark Cave-Ayland
>>  *
>>  * This represents the Sparc32 lance (Am7990) ethernet device which is
>>  * an earlier register-compatible member of the AMD PC-Net II
>>  * (Am79C970A) family.
>>
>> In reality pcnet.c/pcnet.h are just the inner workings of the pcnet-pci
>> and lance devices. The comments in pcnet-pci.c and lance.c are identical
>> except for the Sparc32 reference and it was the same header from
>> pcnet-pci.c that I used as the basis for my last patch.
> 
> You are right the PCnet family is based on the Lance one, but it seems
> nobody remembers the Lance origin, the "PC-Net" took over.
> 
> Maybe we can agree with the different families having an unique
> "hw/net/pcnet_lance.h" header with all Lance/PC-Net related XXX_TYPEs,
> what do you think?

This is definitely a good idea in principle, however the lance device in
its current form cannot work for anything other than SPARC32 because of
the the word-size byte swaps for FIFO transfers which occur for DMA
transfers (see the code for ledma_memory_read/ledma_memory_write).

I think in its current form the patch allows for someone to potentially
implement this later for other architectures (e.g x86) so while I don't
want to disallow this in future, it isn't really within the scope of
this particular patchset.


ATB,

Mark.