Re: [RFC PATCH v2 04/11] PCI/P2PDMA: Introduce pci_p2pdma_should_map_bus() and pci_p2pdma_bus_offset()

[Christoph Hellwig]

On Thu, Mar 11, 2021 at 04:31:34PM -0700, Logan Gunthorpe wrote:
> Introduce pci_p2pdma_should_map_bus() which is meant to be called by
> DMA map functions to determine how to map a given p2pdma page.
> 
> pci_p2pdma_bus_offset() is also added to allow callers to get the bus
> offset if they need to map the bus address.
> 
> Signed-off-by: Logan Gunthorpe <logang@xxxxxxxxxxxx>
> ---
>  drivers/pci/p2pdma.c       | 50 ++++++++++++++++++++++++++++++++++++++
>  include/linux/pci-p2pdma.h | 11 +++++++++
>  2 files changed, 61 insertions(+)
> 
> diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
> index 7f6836732bce..66d16b7eb668 100644
> --- a/drivers/pci/p2pdma.c
> +++ b/drivers/pci/p2pdma.c
> @@ -912,6 +912,56 @@ void pci_p2pdma_unmap_sg_attrs(struct device *dev, struct scatterlist *sg,
>  }
>  EXPORT_SYMBOL_GPL(pci_p2pdma_unmap_sg_attrs);
>  
> +/**
> + * pci_p2pdma_bus_offset - returns the bus offset for a given page
> + * @page: page to get the offset for
> + *
> + * Must be passed a PCI p2pdma page.
> + */
> +u64 pci_p2pdma_bus_offset(struct page *page)
> +{
> +	struct pci_p2pdma_pagemap *p2p_pgmap = to_p2p_pgmap(page->pgmap);
> +
> +	WARN_ON(!is_pci_p2pdma_page(page));
> +
> +	return p2p_pgmap->bus_offset;
> +}
> +EXPORT_SYMBOL_GPL(pci_p2pdma_bus_offset);

I don't see why this would be exported.  

> +EXPORT_SYMBOL_GPL(pci_p2pdma_dma_map_type);

Same here.  Also the two helpers don't really look very related.

I suspect you really want to move the p2p handling bits currenly added
to kernel/dma/direct.c into drivers/pci/p2pdma.c instead, as that will
allow direct access to the pci_p2pdma_pagemap and should thus simplify
things quite a bit.