Messages in this thread | | | From | Logan Gunthorpe <> | Date | Wed, 29 Sep 2021 15:15:34 -0600 | Subject | Re: [PATCH v3 01/20] lib/scatterlist: add flag for indicating P2PDMA segments in an SGL |
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On 2021-09-28 12:32 p.m., Jason Gunthorpe wrote: > On Thu, Sep 16, 2021 at 05:40:41PM -0600, Logan Gunthorpe wrote: >> config PCI_P2PDMA >> bool "PCI peer-to-peer transfer support" >> - depends on ZONE_DEVICE >> + depends on ZONE_DEVICE && 64BIT > > Perhaps a comment to explain what the 64bit is doing?
Added.
>> 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 266754a55327..e62b1cf6386f 100644 >> +++ b/include/linux/scatterlist.h >> @@ -64,6 +64,21 @@ struct sg_append_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_DMA_PCI_P2PDMA 0x04UL > > Add a > static_assert(__alignof__(void *) == 8); > > ?
Good idea. Though, I think your line isn't quite correct. I've added:
static_assert(__alignof__(struct page) >= 8);
>> +#define sg_is_dma_pci_p2pdma(sg) ((sg)->page_link & SG_DMA_PCI_P2PDMA) > > I've been encouraging people to use static inlines more..
I also prefer static inlines, but I usually follow the style of the code I'm changing. In any case, I've changed to static inlines similar to your example.
>> /** >> * sg_assign_page - Assign a given page to an SG entry >> @@ -86,13 +103,13 @@ struct sg_append_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; > > I think this should just be '& SG_END', sg_assign_page() doesn't look > like it should ever be used on a sg_chain entry, so this is just > trying to preserve the end stamp.
Perhaps, but I'm not comfortable making that change in this patch or series. Though, I've reverted this specific change in my patch so sg_assign_page() will clear SG_DMA_PCI_P2PDMA.
Logan
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