linux-kernel - Re: [PATCH v3 1/7] device: introduce per device dma_pfn

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Date:	Thu, 1 May 2014 20:01:09 -0500
From:	Rob Herring <robherring2@...il.com>
To:	Santosh Shilimkar <santosh.shilimkar@...com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Russell King <linux@....linux.org.uk>,
	Arnd Bergmann <arnd@...db.de>, Olof Johansson <olof@...om.net>,
	Grant Likely <grant.likely@...aro.org>,
	Rob Herring <robh+dt@...nel.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Linus Walleij <linus.walleij@...aro.org>,
	Grygorii Strashko <grygorii.strashko@...com>
Subject: Re: [PATCH v3 1/7] device: introduce per device dma_pfn_offset

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

Reviewed-by: Rob Herring <robh@...nel.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
>
--
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