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Message-ID: <56301E24.1060304@ozlabs.ru> Date: Wed, 28 Oct 2015 12:00:20 +1100 From: Alexey Kardashevskiy <aik@...abs.ru> To: Nishanth Aravamudan <nacc@...ux.vnet.ibm.com> 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 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. > > 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). -- Alexey -- 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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