Messages in this thread | | | Date | Wed, 3 Mar 2004 17:38:29 -0800 (PST) | From | Matthew Jacob <> | Subject | Re: [BUG?] Recent feral ISP interaction with alpha dma |
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Thanks for spotting this...
Hmm- I guess I never really asked anyone what sg_dma_len was supposed to apply to.
The best comment about this seems to be in the mips header
/* * These macros should be used after a pci_map_sg call has been done * to get bus addresses of each of the SG entries and their lengths. * You should only work with the number of sg entries pci_map_sg * returns, or alternatively stop on the first sg_dma_len(sg) which * is 0. */
So- I believe I'm using it correctly (well, not quite as I'm not checking for a length of zero) - I call pci_map_sg, and for each platform I should be using sg_dma_len- after all, there may be architectures which don't have sg->length.
The scatterlist code in sg_classify isn't quite what you need to look at- this sets up some kind of private scheme in alpha which then gets decoded into an output list in sg_fill where it looks like more dma_length entries get filled than the 'leader'.
I just gave away my Alphaserver 4100, but I know that the 2.4.18 kernels used to work with my stuff on it- I wonder what the real issue is?
On Wed, 3 Mar 2004, Bailey, Scott wrote:
> Here's a weird problem for which I maybe have an answer except I'm not sure > if it's right. Hopefully the "many eyes" safety net will stop me from doing > anything truly stupid. :-) > > I have an Alphaserver 4100 where I have been testing a build of kernel > 2.4.24 with the most recent snapshot of the feral isp driver. (A previous > release of the driver, patched onto 2.4.22, is running great but I want to > get onto the newer kernel.) > > The system boots happily enough, but eventually I start seeing sequences of: > > pci_map_sg failed: could not allocate dma page tables > isp2: unable to dma map request > > and processes start wedging. > > After poking around in the source, I am suspecting my problem in the feral > isp_pci.c:tdma_mk() where a little snippet goes: > > while (resid > 0) { > nseg++; > resid -= sg_dma_len(sg); > sg++; > } > > The previous (working) version of this code is: > > while (resid > 0) { > nseg++; > resid -= sg->length; > sg++; > } > > The problem is, that looking at arch/alpha/kernel/pci_iommu.c:sg_classify() > in the recent 2.4 kernels, I see that sg->dma_length only gets filled in for > scatterlist elements that are leaders. I suspect the non-leader elements > contain crud that confuse the resid count in unpredictable ways. > > The question for everybody: is it better to fix this by reverting the > isp_pci.c stuff to refer to sg->length again instead of sg->dma_length, so > that I'm always referencing a valid quantity, or should I tweak pci_iommu.c > so it sets this value to 0 for non-leader elements (and ignore the fact that > code may still not be paying attention to sg->dma_address before making > decisions about the element)? > > I couldn't figure out what other architectures were doing from sniffing > around the other directories. > > What will break the least? :-) > > Thanks, > > Scott Bailey > scott <dot> bailey <at> eds <dot> com > - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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