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

Rob Herring
2014-05-02T01:01:12Z

On Thu, Apr 24, 2014 at 10:30 AM, Santosh Shilimkar
<santosh.shilimkar@ti.com> 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@linuxfoundation.org>
> Cc: Russell King <linux@arm.linux.org.uk>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Olof Johansson <olof@lixom.net>
> Cc: Grant Likely <grant.likely@linaro.org>
> Cc: Rob Herring <robh+dt@kernel.org>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Linus Walleij <linus.walleij@linaro.org>
> Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
> Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>

Reviewed-by: Rob Herring <robh@kernel.org>

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
>