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Message-ID: <b811f66d-2353-23c6-c9fa-e279cdb0f832@shipmail.org>
Date: Tue, 8 Oct 2019 14:34:17 +0200
From: Thomas Hellström (VMware)
<thomas_os@...pmail.org>
To: Christoph Hellwig <hch@...radead.org>,
Christian König <christian.koenig@....com>
Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: dma coherent memory user-space maps
Hi, Christoph,
Following our previous discussion I wonder if something along the lines
of the following could work / be acceptible
typedef unsigned long dma_pfn_t /* Opaque pfn type. Arch dependent. This
could if needed be a struct with a pointer and an offset */
/* Similar to vmf_insert_mixed() */
vm_fault_t dma_vmf_insert_mixed(struct device *dev,
struct vm_area_struct *vma,
unsigned long addr,
dma_pfn_t dpfn,
unsigned long attrs);
/* Similar to vmf_insert_pfn_pmd() */
vm_fault_t dma_vmf_insert_pfn_pmd(struct device *dev,
struct vm_area_struct *vma,
unsigned long addr,
dma_pfn_t dpfn,
unsigned long attrs);
/* Like vmap, but takes struct dma_pfns. */
extern void *dma_vmap(struct device *dev,
dma_pfn_t dpfns[],
unsigned int count, unsigned long flags,
unsigned long attrs);
/* Obtain struct dma_pfn pointers from a dma coherent allocation */
int dma_get_dpfns(struct device *dev, void *cpu_addr, dma_addr_t dma_addr,
pgoff_t offset, pgoff_t num, dma_pfn_t dpfns[]);
I figure, for most if not all architectures we could use an ordinary pfn
as dma_pfn_t, but the dma layer would still have control over how those
pfns are obtained and how they are used in the kernel's mapping APIs.
If so, I could start looking at this, time permitting, for the cases
where the pfn can be obtained from the kernel address or from
arch_dma_coherent_to_pfn(), and also the needed work to have a tailored
vmap_pfn().
Thanks,
/Thomas
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