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Message-ID: <20151028015451.GH7716@linux.vnet.ibm.com> Date: Tue, 27 Oct 2015 18:54:51 -0700 From: Nishanth Aravamudan <nacc@...ux.vnet.ibm.com> To: Alexey Kardashevskiy <aik@...abs.ru> Cc: Michael Ellerman <mpe@...erman.id.au>, Matthew Wilcox <willy@...ux.intel.com>, Keith Busch <keith.busch@...el.com>, Benjamin Herrenschmidt <benh@...nel.crashing.org>, Paul Mackerras <paulus@...ba.org>, David Gibson <david@...son.dropbear.id.au>, Christoph Hellwig <hch@...radead.org>, "David S. Miller" <davem@...emloft.net>, linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org, sparclinux@...r.kernel.org Subject: Re: [PATCH 2/7 v2] powerpc/dma-mapping: override dma_get_page_shift On 28.10.2015 [12:00:20 +1100], Alexey Kardashevskiy wrote: > On 10/28/2015 09:27 AM, Nishanth Aravamudan wrote: > >On 27.10.2015 [17:02:16 +1100], Alexey Kardashevskiy wrote: > >>On 10/24/2015 07:57 AM, Nishanth Aravamudan wrote: > >>>On Power, the kernel's page size can differ from the IOMMU's page size, > >>>so we need to override the generic implementation, which always returns > >>>the kernel's page size. Lookup the IOMMU's page size from struct > >>>iommu_table, if available. Fallback to the kernel's page size, > >>>otherwise. > >>> > >>>Signed-off-by: Nishanth Aravamudan <nacc@...ux.vnet.ibm.com> > >>>--- > >>> arch/powerpc/include/asm/dma-mapping.h | 3 +++ > >>> arch/powerpc/kernel/dma.c | 9 +++++++++ > >>> 2 files changed, 12 insertions(+) > >>> > >>>diff --git a/arch/powerpc/include/asm/dma-mapping.h b/arch/powerpc/include/asm/dma-mapping.h > >>>index 7f522c0..c5638f4 100644 > >>>--- a/arch/powerpc/include/asm/dma-mapping.h > >>>+++ b/arch/powerpc/include/asm/dma-mapping.h > >>>@@ -125,6 +125,9 @@ static inline void set_dma_offset(struct device *dev, dma_addr_t off) > >>> #define HAVE_ARCH_DMA_SET_MASK 1 > >>> extern int dma_set_mask(struct device *dev, u64 dma_mask); > >>> > >>>+#define HAVE_ARCH_DMA_GET_PAGE_SHIFT 1 > >>>+extern unsigned long dma_get_page_shift(struct device *dev); > >>>+ > >>> #include <asm-generic/dma-mapping-common.h> > >>> > >>> extern int __dma_set_mask(struct device *dev, u64 dma_mask); > >>>diff --git a/arch/powerpc/kernel/dma.c b/arch/powerpc/kernel/dma.c > >>>index 59503ed..e805af2 100644 > >>>--- a/arch/powerpc/kernel/dma.c > >>>+++ b/arch/powerpc/kernel/dma.c > >>>@@ -335,6 +335,15 @@ int dma_set_mask(struct device *dev, u64 dma_mask) > >>> } > >>> EXPORT_SYMBOL(dma_set_mask); > >>> > >>>+unsigned long dma_get_page_shift(struct device *dev) > >>>+{ > >>>+ struct iommu_table *tbl = get_iommu_table_base(dev); > >>>+ if (tbl) > >>>+ return tbl->it_page_shift; > >> > >> > >>All PCI devices have this initialized on POWER (at least, our, IBM's > >>POWER) so 4K will always be returned here while in the case of > >>(get_dma_ops(dev)==&dma_direct_ops) it could actually return > >>PAGE_SHIFT. Is 4K still preferred value to return here? > > > >Right, so the logic of my series, goes like this: > > > >a) We currently are assuming DMA_PAGE_SHIFT (conceptual constant) is > >PAGE_SHIFT everywhere, including Power. > > > >b) After 2/7, the Power code will return either the IOMMU table's shift > >value, if set, or PAGE_SHIFT (I guess this would be the case if > >get_dma_ops(dev) == &dma_direct_ops, as you said). That is no different > >than we have now, except we can return the accurate IOMMU value if > >available. > > If it is not available, then something went wrong and BUG_ON(!tbl || > !tbl->it_page_shift) make more sense here than pretending that this > function can ever return PAGE_SHIFT. imho. That's a good point, thanks! > >3) After 3/7, the platform can override the generic Power > >get_dma_page_shift(). > > > >4) After 4/7, pseries will return the DDW value, if available, then > >fallback to the IOMMU table's value. I think in the case of > >get_dma_ops(dev)==&dma_direct_ops, the only way that can happen is if we > >are using DDW, right? > > This is for pseries guests; for the powernv host it is a "bypass" > mode which does 64bit direct DMA mapping and there is no additional > window for that (i.e. DIRECT64_PROPNAME, etc). You're right! I should update the code to handle both cases. In "bypass" mode, what TCE size is used? Is it guaranteed to be 4K? Seems like this would be a different platform implentation I'd put in for 'powernv', is that right? My apologies for missing that, and thank you for the review! -Nish -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.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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