linux-kernel - Re: [PATCH RFC 51/51] ARM: 7805/1: mm: change max*pfn to include the physical offset of memory

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Date:	Mon, 5 Aug 2013 22:15:11 -0500
From:	Rob Herring <robherring2@...il.com>
To:	Santosh Shilimkar <santosh.shilimkar@...com>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH RFC 51/51] ARM: 7805/1: mm: change max*pfn to include the
 physical offset of memory

On Thu, Aug 1, 2013 at 5:25 PM, Santosh Shilimkar
<santosh.shilimkar@...com> wrote:
> Most of the kernel code assumes that max*pfn is maximum pfns because
> the physical start of memory is expected to be PFN0. Since this
> assumption is not true on ARM architectures, the meaning of max*pfn
> is number of memory pages. This is done to keep drivers happy which
> are making use of of these variable to calculate the dma bounce limit
> using dma_mask.
>
> Now since we have a architecture override possibility for DMAable
> maximum pfns, lets make meaning of max*pfns as maximum pnfs on ARM
> as well.
>
> Signed-off-by: Santosh Shilimkar <santosh.shilimkar@...com>
> Signed-off-by: Russell King <rmk+kernel@....linux.org.uk>
> ---
>  arch/arm/include/asm/dma-mapping.h |    8 ++++++++
>  arch/arm/mm/init.c                 |   10 ++++------
>  2 files changed, 12 insertions(+), 6 deletions(-)
>
> diff --git a/arch/arm/include/asm/dma-mapping.h b/arch/arm/include/asm/dma-mapping.h
> index 5b579b9..863cd84 100644
> --- a/arch/arm/include/asm/dma-mapping.h
> +++ b/arch/arm/include/asm/dma-mapping.h
> @@ -64,6 +64,7 @@ static inline dma_addr_t virt_to_dma(struct device *dev, void *addr)
>  {
>         return (dma_addr_t)__virt_to_bus((unsigned long)(addr));
>  }
> +
>  #else
>  static inline dma_addr_t pfn_to_dma(struct device *dev, unsigned long pfn)
>  {
> @@ -86,6 +87,13 @@ static inline dma_addr_t virt_to_dma(struct device *dev, void *addr)
>  }
>  #endif
>
> +/* The ARM override for dma_max_pfn() */
> +static inline unsigned long dma_max_pfn(struct device *dev)
> +{
> +       return PHYS_PFN_OFFSET + dma_to_pfn(dev, *dev->dma_mask);

Do we need to handle dev == NULL case?

Rob
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