[Qemu-devel] Re: PCNet and Lance merge, almost there

[Fabrice Bellard]

Blue Swirl wrote:
> Hi,
>
> I got PCNet working in Sun4m architecture by fixing endianness problems 
> and adding IOMMU hooks. There are still some endianness issues, that's 
> why I disabled the address matching code.
>
> The original code could benefit from some touchup and performance tuning.
>
> Any comments?

- A general remark : instead of using SPARC_IOMMU_TRANSLATE, you should 
use new memory helpers to read or write bytes such as 
pcnet_physical_memory_read() and pcnet_physical_memory_write(). The 
rationale is that ultimately pci memory accesses will also use PCI 
specific I/Os to handle the case where the PCI memory is not mapped 
directly in the CPU address space. For the sparc iommu you should define 
global helpers such as sparc_iommu_memory_read() and 
sparc_iommu_memory_write().

- CPU specific #ifdefs (or CPU specific endianness macros) should be 
avoided in device code unless it is really necessary. The rationale is 
that ultimately there will be a single QEMU executable supporting all 
machines and CPUs. In the pcnet case for example, the macro 
'SPARC_FIX_DESC' is almost surely not necessary because the device seems 
implicitely little endian (the original code lacks correct endianness 
conversion routines !).

Regards,

Fabrice.