On Fri, Jun 11, 2010 at 11:55:07AM -0600, Scott Long wrote: > 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.
I guess many PCIe drivers in tree do not explicitly set 4GB boundary restriction. Isn't it better to set it automatically with bus_get_dma_tag(9)? > > Scott > > _______________________________________________ svn-src-all@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org"
