Re: General porting question

On Thu, Oct 09, 2003 at 12:11:09PM +0800, Jacky Lam wrote:

Dear all,

    Could anyone give me some notes/idea what should be take care to port an
x86 PCI card driver to powerpc walnut platform? I try several
cards(ethernet, audio) which run well on my PC by cross-compiling the
drivers. They can be recognized successfully, but none of them works. Walnut
seems don't be able to receive any interrupt from the cards.

    I guess there must be something about PCI implementation in PPC
different from x86. Is there any expert on PPC PCI can tell me what happen?
Or any related documentation can help?

Documentation/DMA-mapping.txt and IO-mapping.txt are of general
interest when dealing with DMA capable devices and address translation.
Unfortunately, the docs/APIs aren't yet complete with respect to some
platforms. On non cache coherent processors like PPC4xx/8xx, consistent
memory is allocated from vmalloc space.  The virt_to_*/*_to_virt family
of APIs is only valid for staticly mapped kernel system memory addresses
(KERNELBASE -> KERNELBASE+<size of sysmem>).

A quick inspection shows that es1371 does some things that won't work on
a 405.  It takes a pci_alloc_consistent buffer and does a virt_to_page.
That will be bogus since the buffer's virtual address is in vmalloc
space on 4xx.  In addition, it performs a virt_to_phys and then uses
remap_page_range on that...that will be bogus as well.  A bus_to_virt
on the pci_alloc_consistent buffer's dma_addr will work and then
virt_to_page() can be used on that virtual address.  In the same
fashion one could do a virt_to_phys(bus_to_virt(dma_addr) to get
the correct physical address to be passed to remap_page_range.

Someday we will get the DMA API to be completely cross architecture
so driver. It's much better than the situation in older kernels. :)

On the other hand, emu10k1 works out of the box...SB Live.

-Matt

** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/

A quick inspection shows that es1371 does some things that won't work on
a 405.  It takes a pci_alloc_consistent buffer and does a virt_to_page.
That will be bogus since the buffer's virtual address is in vmalloc
space on 4xx.  In addition, it performs a virt_to_phys and then uses
remap_page_range on that...that will be bogus as well.  A bus_to_virt
on the pci_alloc_consistent buffer's dma_addr will work and then
virt_to_page() can be used on that virtual address.  In the same
fashion one could do a virt_to_phys(bus_to_virt(dma_addr) to get
the correct physical address to be passed to remap_page_range.

    That means in short:

    pci_alloc_consistent() ->virt_to_page() should be replaced by
pci_alloc_consistent()->bus_to_virt()->virt_to_page().

    Similarly, for any PCI related memory space. Before using
virt_to_*/*_to_virt(), I should use bus_to_*/*_to_bus() on the argument
first.

    Is it right?

    Thanks for your help.

Best regards,
Jacky


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