Messages in this thread |  | | Subject | Re: [PATCH 06/16] lib/scatterlist: Add flag for indicating P2PDMA segments in an SGL | From | John Hubbard <> | Date | Sun, 2 May 2021 15:34:17 -0700 |
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On 4/8/21 10:01 AM, Logan Gunthorpe wrote: > Make use of the third free LSB in scatterlist's page_link on 64bit systems. > > The extra bit will be used by dma_[un]map_sg_p2pdma() to determine when a > given SGL segments dma_address points to a PCI bus address. > dma_unmap_sg_p2pdma() will need to perform different cleanup when a > segment is marked as P2PDMA. > > Using this bit requires adding an additional dependency on CONFIG_64BIT to > CONFIG_PCI_P2PDMA. This should be acceptable as the majority of P2PDMA > use cases are restricted to newer root complexes and roughly require the > extra address space for memory BARs used in the transactions.
Totally agree with the CONFIG_64BIT call.
Also, I have failed to find anything wrong with this patch. :)
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
thanks, -- John Hubbard NVIDIA
> > Signed-off-by: Logan Gunthorpe <logang@deltatee.com> > --- > drivers/pci/Kconfig | 2 +- > include/linux/scatterlist.h | 49 ++++++++++++++++++++++++++++++++++--- > 2 files changed, 46 insertions(+), 5 deletions(-) > > diff --git a/drivers/pci/Kconfig b/drivers/pci/Kconfig > index 0c473d75e625..90b4bddb3300 100644 > --- a/drivers/pci/Kconfig > +++ b/drivers/pci/Kconfig > @@ -163,7 +163,7 @@ config PCI_PASID > > config PCI_P2PDMA > bool "PCI peer-to-peer transfer support" > - depends on ZONE_DEVICE > + depends on ZONE_DEVICE && 64BIT > select GENERIC_ALLOCATOR > help > Enableѕ drivers to do PCI peer-to-peer transactions to and from > diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h > index 6f70572b2938..5525d3ebf36f 100644 > --- a/include/linux/scatterlist.h > +++ b/include/linux/scatterlist.h > @@ -58,6 +58,21 @@ struct sg_table { > #define SG_CHAIN 0x01UL > #define SG_END 0x02UL > > +/* > + * bit 2 is the third free bit in the page_link on 64bit systems which > + * is used by dma_unmap_sg() to determine if the dma_address is a PCI > + * bus address when doing P2PDMA. > + * Note: CONFIG_PCI_P2PDMA depends on CONFIG_64BIT because of this. > + */ > + > +#ifdef CONFIG_PCI_P2PDMA > +#define SG_PCI_P2PDMA 0x04UL > +#else > +#define SG_PCI_P2PDMA 0x00UL > +#endif > + > +#define SG_PAGE_LINK_MASK (SG_CHAIN | SG_END | SG_PCI_P2PDMA) > + > /* > * We overload the LSB of the page pointer to indicate whether it's > * a valid sg entry, or whether it points to the start of a new scatterlist. > @@ -65,8 +80,9 @@ struct sg_table { > */ > #define sg_is_chain(sg) ((sg)->page_link & SG_CHAIN) > #define sg_is_last(sg) ((sg)->page_link & SG_END) > +#define sg_is_pci_p2pdma(sg) ((sg)->page_link & SG_PCI_P2PDMA) > #define sg_chain_ptr(sg) \ > - ((struct scatterlist *) ((sg)->page_link & ~(SG_CHAIN | SG_END))) > + ((struct scatterlist *) ((sg)->page_link & ~SG_PAGE_LINK_MASK)) > > /** > * sg_assign_page - Assign a given page to an SG entry > @@ -80,13 +96,13 @@ struct sg_table { > **/ > static inline void sg_assign_page(struct scatterlist *sg, struct page *page) > { > - unsigned long page_link = sg->page_link & (SG_CHAIN | SG_END); > + unsigned long page_link = sg->page_link & SG_PAGE_LINK_MASK; > > /* > * In order for the low bit stealing approach to work, pages > * must be aligned at a 32-bit boundary as a minimum. > */ > - BUG_ON((unsigned long) page & (SG_CHAIN | SG_END)); > + BUG_ON((unsigned long) page & SG_PAGE_LINK_MASK); > #ifdef CONFIG_DEBUG_SG > BUG_ON(sg_is_chain(sg)); > #endif > @@ -120,7 +136,7 @@ static inline struct page *sg_page(struct scatterlist *sg) > #ifdef CONFIG_DEBUG_SG > BUG_ON(sg_is_chain(sg)); > #endif > - return (struct page *)((sg)->page_link & ~(SG_CHAIN | SG_END)); > + return (struct page *)((sg)->page_link & ~SG_PAGE_LINK_MASK); > } > > /** > @@ -222,6 +238,31 @@ static inline void sg_unmark_end(struct scatterlist *sg) > sg->page_link &= ~SG_END; > } > > +/** > + * sg_mark_pci_p2pdma - Mark the scatterlist entry for PCI p2pdma > + * @sg: SG entryScatterlist > + * > + * Description: > + * Marks the passed in sg entry to indicate that the dma_address is > + * a PCI bus address. > + **/ > +static inline void sg_mark_pci_p2pdma(struct scatterlist *sg) > +{ > + sg->page_link |= SG_PCI_P2PDMA; > +} > + > +/** > + * sg_unmark_pci_p2pdma - Unmark the scatterlist entry for PCI p2pdma > + * @sg: SG entryScatterlist > + * > + * Description: > + * Clears the PCI P2PDMA mark > + **/ > +static inline void sg_unmark_pci_p2pdma(struct scatterlist *sg) > +{ > + sg->page_link &= ~SG_PCI_P2PDMA; > +} > + > /** > * sg_phys - Return physical address of an sg entry > * @sg: SG entry >
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