Re: [PATCH v3 1/7] device: introduce per device dma_pfn_offset

[Rob Herring]

On Thu, Apr 24, 2014 at 10:30 AM, Santosh Shilimkar
<santosh.shilimkar@xxxxxx> wrote:
> On few architectures, there are few restrictions on DMAble area of system
> RAM. That also means that devices needs to know about this restrictions so
> that the dma_masks can be updated accordingly and dma address translation
> helpers can add/subtract the dma offset.
>
> In most of cases DMA addresses can be performed using offset value of
> Bus address space relatively to physical address space as following:
>
> PFN->DMA:  __pfn_to_phys(pfn + [-]dma_pfn_offset)
> DMA->PFN:  __phys_to_pfn(dma_addr) + [-]dma_pfn_offset
>
> So we introduce per device dma_pfn_offset which can be popullated
> by architecture init code while creating the devices.
>
> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Cc: Russell King <linux@xxxxxxxxxxxxxxxx>
> Cc: Arnd Bergmann <arnd@xxxxxxxx>
> Cc: Olof Johansson <olof@xxxxxxxxx>
> Cc: Grant Likely <grant.likely@xxxxxxxxxx>
> Cc: Rob Herring <robh+dt@xxxxxxxxxx>
> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> Cc: Linus Walleij <linus.walleij@xxxxxxxxxx>
> Signed-off-by: Grygorii Strashko <grygorii.strashko@xxxxxx>
> Signed-off-by: Santosh Shilimkar <santosh.shilimkar@xxxxxx>

Reviewed-by: Rob Herring <robh@xxxxxxxxxx>

Rob

> ---
>  include/linux/device.h |    2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/include/linux/device.h b/include/linux/device.h
> index 233bbbe..85a52d6 100644
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -691,6 +691,7 @@ struct acpi_dev_node {
>   * @coherent_dma_mask: Like dma_mask, but for alloc_coherent mapping as not all
>   *             hardware supports 64-bit addresses for consistent allocations
>   *             such descriptors.
> + * @dma_pfn_offset: offset of DMA memory range relatively of RAM
>   * @dma_parms: A low level driver may set these to teach IOMMU code about
>   *             segment limitations.
>   * @dma_pools: Dma pools (if dma'ble device).
> @@ -756,6 +757,7 @@ struct device {
>                                              not all hardware supports
>                                              64 bit addresses for consistent
>                                              allocations such descriptors. */
> +       unsigned long   dma_pfn_offset;
>
>         struct device_dma_parameters *dma_parms;
>
> --
> 1.7.9.5
>
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