svn commit: r209026 - in head/sys/ia64: ia64 include

[Scott Long]

On Jun 11, 2010, at 11:53 AM, Marcel Moolenaar wrote:
> 
> On Jun 11, 2010, at 10:47 AM, Scott Long wrote:
> 
>> On Jun 11, 2010, at 11:44 AM, Marcel Moolenaar wrote:
>>> 
>>> On Jun 11, 2010, at 10:37 AM, Scott Long wrote:
>>>> 
>>>> I'm not clear why you even need bounce buffers for RX.  The chip supports 64bit addresses with no boundary or alignment restrictions.
>>> 
>>> As per:
>>>      /*
>>>       * All controllers that are not 5755 or higher have 4GB
>>>       * boundary DMA bug.
>>>       * Whenever an address crosses a multiple of the 4GB boundary
>>>       * (including 4GB, 8Gb, 12Gb, etc.) and makes the transition
>>>       * from 0xX_FFFF_FFFF to 0x(X+1)_0000_0000 an internal DMA
>>>       * state machine will lockup and cause the device to hang.
>>>       */
>>>      if (BGE_IS_5755_PLUS(sc) == 0)
>>>              sc->bge_flags |= BGE_FLAG_4G_BNDRY_BUG;
>>> 
>>> and:
>>>      lowaddr = BUS_SPACE_MAXADDR;
>>>      if ((sc->bge_flags & BGE_FLAG_40BIT_BUG) != 0)
>>>              lowaddr = BGE_DMA_MAXADDR;
>>>      if ((sc->bge_flags & BGE_FLAG_4G_BNDRY_BUG) != 0)
>>>              lowaddr = BUS_SPACE_MAXADDR_32BIT;
>>>      /*
>>>       * Allocate the parent bus DMA tag appropriate for PCI.
>>>       */
>>>      error = bus_dma_tag_create(bus_get_dma_tag(sc->bge_dev),
>>>          1, 0, lowaddr, BUS_SPACE_MAXADDR, NULL,
>>>          NULL, BUS_SPACE_MAXSIZE_32BIT, 0, BUS_SPACE_MAXSIZE_32BIT,
>>>          0, NULL, NULL, &sc->bge_cdata.bge_parent_tag);
>>> 
>>> 
>> 
>> Noted in previous email.  If this restriction is put in the boundary attribute, then you'll only bounce the very rare case of an mbuf straddling a 4G boundary.
> 
> I agree with you, but I was just giving the facts. I don't even
> know if we attempted to use the boundary argument before but
> problems forced us to resort to this.
> 

Thanks to the design limitation of PCIe, the 4GB boundary is a common restriction and should work fine in FreeBSD.

Scott