linux-kernel - Re: [PATCH 2/3] swiotlb: prefix dma_to_phys and phys_to

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Message-ID: <CACJDEmrzKOExg-Rchjy2hfVzkzbCZ=WNn4Bu3EVgim748VvRig@mail.gmail.com>
Date:	Mon, 28 Mar 2016 14:29:29 -0400
From:	Konrad Rzeszutek Wilk <konrad@...nel.org>
To:	Sinan Kaya <okaya@...eaurora.org>
Cc:	Robin Murphy <robin.murphy@....com>,
	linux-arm-kernel@...ts.infradead.org, timur@...eaurora.org,
	cov@...eaurora.org, nwatters@...eaurora.org,
	linux-mips@...ux-mips.org, linux-ia64@...r.kernel.org,
	linux-xtensa@...ux-xtensa.org,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Max Filippov <jcmvbkbc@...il.com>,
	Chris Metcalf <cmetcalf@...hip.com>,
	Paul Mackerras <paulus@...ba.org>,
	"H. Peter Anvin" <hpa@...or.com>, Huacai Chen <chenhc@...ote.com>,
	Guan Xuetao <gxt@...c.pku.edu.cn>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Jisheng Zhang <jszhang@...vell.com>,
	Florian Fainelli <f.fainelli@...il.com>,
	Russell King <linux@....linux.org.uk>,
	Aaro Koskinen <aaro.koskinen@....fi>,
	Michael Ellerman <mpe@...erman.id.au>, X86 <x86@...nel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Guenter Roeck <linux@...ck-us.net>,
	Fenghua Yu <fenghua.yu@...el.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Arnd Bergmann <arnd@...db.de>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Akinobu Mita <akinobu.mita@...il.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Valentin Rothberg <valentinrothberg@...il.com>,
	Chris Zankel <chris@...kel.net>,
	Tony Luck <tony.luck@...el.com>, linux-pci@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, Dean Nelson <dnelson@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Ralf Baechle <ralf@...ux-mips.org>,
	"Suthikulpanit, Suravee" <Suravee.Suthikulpanit@....com>,
	Joe Perches <joe@...ches.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Stefano Stabellini <stefano.stabellini@...citrix.com>
Subject: Re: [PATCH 2/3] swiotlb: prefix dma_to_phys and phys_to_dma functions

On Fri, Mar 18, 2016 at 11:00 AM, Sinan Kaya <okaya@...eaurora.org> wrote:
> On 3/18/2016 8:12 AM, Robin Murphy wrote:
>> Since we know for sure that swiotlb_to_phys is a no-op on arm64, it might be cleaner to simply not reference it at all. I suppose we could have some private local wrappers, e.g.:
>>
>> #define swiotlb_to_virt(addr) phys_to_virt((phys_addr_t)(addr))
>>
>> to keep the intent of the code clear (and just in case anyone ever builds a system mad enough to warrant switching out that definition, but I'd hope that never happens).
>>
>> Otherwise, looks good - thanks for doing this!
>
> OK. I added this. Reviewed-by?
>
> I'm not happy to submit such a big patch for all different ARCHs. I couldn't
> find a cleaner solution. I'm willing to split this patch into multiple if there
> is a better way.
>
> diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c
> index ada00c3..8c0f66b 100644
> --- a/arch/arm64/mm/dma-mapping.c
> +++ b/arch/arm64/mm/dma-mapping.c
> @@ -29,6 +29,14 @@
>
>  #include <asm/cacheflush.h>
>
> +/*
> + * If you are building a system without IOMMU, then you are using SWIOTLB
> + * library. The ARM64 adaptation of this library does not support address
> + * translation and it assumes that physical address = dma address for such
> + * a use case. Please don't build a platform that violates this.
> + */

Why not just expand the ARM64 part to support address translation?

> +#define swiotlb_to_virt(addr) phys_to_virt((phys_addr_t)(addr))
> +

Adding Stefano here.

>  static pgprot_t __get_dma_pgprot(struct dma_attrs *attrs, pgprot_t prot,
>                                  bool coherent)
>  {
> @@ -188,7 +196,7 @@ static void __dma_free(struct device *dev, size_t size,
>                        void *vaddr, dma_addr_t dma_handle,
>                        struct dma_attrs *attrs)
>  {
> -       void *swiotlb_addr = phys_to_virt(swiotlb_dma_to_phys(dev, dma_handle));
> +       void *swiotlb_addr = swiotlb_to_virt(dma_handle);
>
>         size = PAGE_ALIGN(size);
>
> @@ -209,8 +217,7 @@ static dma_addr_t __swiotlb_map_page(struct device *dev, struct page *page,
>
>         dev_addr = swiotlb_map_page(dev, page, offset, size, dir, attrs);
>         if (!is_device_dma_coherent(dev))
> -               __dma_map_area(phys_to_virt(swiotlb_dma_to_phys(dev, dev_addr)),
> -                              size, dir);
> +               __dma_map_area(swiotlb_to_virt(dev_addr), size, dir);
>
>         return dev_addr;
>  }
> @@ -283,8 +290,7 @@ static void __swiotlb_sync_single_for_device(struct device *dev,
>  {
>         swiotlb_sync_single_for_device(dev, dev_addr, size, dir);
>         if (!is_device_dma_coherent(dev))
> -               __dma_map_area(phys_to_virt(swiotlb_dma_to_phys(dev, dev_addr)),
> -                              size, dir);
> +               __dma_map_area(swiotlb_to_virt(dev_addr), size, dir);
>  }
>
>
>
>
> --
> Sinan Kaya
> Qualcomm Technologies, Inc. on behalf of Qualcomm Innovation Center, Inc.
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project