On 2020-11-10 4:25 p.m., Bjorn Helgaas wrote:
> On Fri, Nov 06, 2020 at 10:00:24AM -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.
>
> s/dma/DMA/ for consistency (also below in function comment)
>
>> 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 | 46 ++++++++++++++++++++++++++++++++++++++
>> include/linux/pci-p2pdma.h | 11 +++++++++
>> 2 files changed, 57 insertions(+)
>>
>> diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
>> index ea8472278b11..9961e779f430 100644
>> --- a/drivers/pci/p2pdma.c
>> +++ b/drivers/pci/p2pdma.c
>> @@ -930,6 +930,52 @@ 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.
>
> s/pci/PCI/
>
>> + */
>> +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);
>> +
>> +/**
>> + * pci_p2pdma_should_map_bus - determine if a dma mapping should use the
>> + * bus address
>> + * @dev: device doing the DMA request
>> + * @pgmap: dev_pagemap structure for the mapping
>> + *
>> + * Returns 1 if the page should be mapped with a bus address, 0 otherwise
>> + * and -1 the device should not be mapping P2PDMA pages.
>
> I think this is missing a word.
>
> I'm not really sure how to interpret the "should" in
> pci_p2pdma_should_map_bus(). If this returns -1, does that mean the
> patches *cannot* be mapped? They *could* be mapped, but you really
> *shouldn't*? Something else?
>
> 1 means page should be mapped with bus address. 0 means ... what,
> exactly? It should be mapped with some different address?
1 means it must be mapped with a bus address
0 means it may be mapped normally (through the IOMMU or just with a
direct physical address)
-1 means it cannot be mapped and should fail (ie. if it must go through
the IOMMU, but the IOMMU is not in the whitelist).
> Sorry these are naive questions because I don't know how all this
> works.
Thanks for the review. Definitely points out some questionable language
that I used. I'll reword this if/when it goes further.
Logan
