[Xen-devel] Re: [PATCH 02/15] [swiotlb] Add swiotlb_engine structure for tracking multiple software IO TLBs.

[Chris Wright <chrisw@xxxxxxxxxxxx>]

* Konrad Rzeszutek Wilk (konrad.wilk@xxxxxxxxxx) wrote:
> The structure contains all of the existing variables used in
> software IO TLB (swiotlb.c) collected within a structure.
> 
> Additionally a name variable and a deconstructor (release) function
> variable is defined for API usages.
> 
> The other set of functions: is_swiotlb_buffer, dma_capable, phys_to_bus,
> bus_to_phys, virt_to_bus, and bus_to_virt server as a method to abstract
> them out of the SWIOTLB library.
> 
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> ---
>  include/linux/swiotlb.h |   94 
> +++++++++++++++++++++++++++++++++++++++++++++++
>  1 files changed, 94 insertions(+), 0 deletions(-)
> 
> diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
> index febedcf..781c3aa 100644
> --- a/include/linux/swiotlb.h
> +++ b/include/linux/swiotlb.h
> @@ -24,6 +24,100 @@ extern int swiotlb_force;
>  
>  extern void swiotlb_init(int verbose);
>  
You can move the comments to a kerneldoc section for proper
documentation.

/**
 * struct swiotlb_engine - short desc...
 * @name:       Name of the engine...
etc

> +struct swiotlb_engine {
> +
> +     /*
> +      * Name of the engine (ie: "Software IO TLB")
> +      */
> +     const char      *name;
> +
> +     /*
> +      * Used to do a quick range check in unmap_single and
> +      * sync_single_*, to see if the memory was in fact allocated by this
> +      * API.
> +      */
> +     char *start;
> +     char *end;

Isn't this still global to swiotlb, not specific to the backend impl.?

> +     /*
> +      * The number of IO TLB blocks (in groups of 64) betweeen start and
> +      * end.  This is command line adjustable via setup_io_tlb_npages.
> +      */
> +     unsigned long nslabs;

Same here.

> +
> +     /*
> +      * When the IOMMU overflows we return a fallback buffer.
> +      * This sets the size.
> +      */
> +     unsigned long overflow;
> +
> +     void *overflow_buffer;

And here.

> +     /*
> +      * This is a free list describing the number of free entries available
> +      * from each index
> +      */
> +     unsigned int *list;
> +
> +     /*
> +      * Current marker in the start through end location. Is incremented
> +      * on each map and wraps around.
> +      */
> +     unsigned int index;
> +
> +     /*
> +      * We need to save away the original address corresponding to a mapped
> +      * entry for the sync operations.
> +      */
> +     phys_addr_t *orig_addr;
> +
> +     /*
> +      * IOMMU private data.
> +      */
> +     void *priv;
> +     /*
> +      * The API call to free a SWIOTLB engine if another wants to register
> +      * (or if want to turn SWIOTLB off altogether).
> +      * It is imperative that this function checks for existing DMA maps
> +      * and not release the IOTLB if there are out-standing maps.
> +      */
> +     int (*release)(struct swiotlb_engine *);
> +
> +     /*
> +      * Is the DMA (Bus) address within our bounce buffer (start and end).
> +      */
> +     int (*is_swiotlb_buffer)(struct swiotlb_engine *, dma_addr_t dev_addr,
> +                              phys_addr_t phys);
> +

Why is this implementation specific?

> +     /*
> +      * Is the DMA (Bus) address reachable by the PCI device?.
> +      */
> +     bool (*dma_capable)(struct device *, dma_addr_t, phys_addr_t, size_t);

This too...

> +     /*
> +      *  Physical to bus (DMA) address translation. On
> +      *  most platforms this is an equivalent function.
> +      */
> +     dma_addr_t (*phys_to_bus)(struct device *hwdev, phys_addr_t paddr);
> +
> +     /*
> +      * Bus (DMA) to physical address translation. On most
> +      * platforms this is an equivalant function.
> +      */
> +     phys_addr_t (*bus_to_phys)(struct device *hwdev, dma_addr_t baddr);
> +
> +     /*
> +      * Virtual to bus (DMA) address translation. On most platforms
> +      * this is a call to __pa(address).
> +      */
> +     dma_addr_t (*virt_to_bus)(struct device *hwdev, void *address);
> +
> +     /*
> +     * Bus (DMA) to virtual address translation. On most platforms
> +     * this is a call to __va(address).
> +     */
> +     void* (*bus_to_virt)(struct device *hwdev, dma_addr_t address);
> +};
> +
>  extern void
>  *swiotlb_alloc_coherent(struct device *hwdev, size_t size,
>                       dma_addr_t *dma_handle, gfp_t flags);
> -- 
> 1.6.2.5

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