linux-kernel - Re: [PATCH -mm 00/12] adds include/asm-generic/pci-dma-common.h

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Date:	Tue, 9 Feb 2010 16:23:35 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	e@....ntt.co.jp
Cc:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	fujita.tomonori@....ntt.co.jp, x86@...nel.org,
	Richard Henderson <rth@...ddle.net>,
	Ivan Kokshaysky <ink@...assic.park.msu.ru>,
	Matt Turner <mattst88@...il.com>,
	Russell King <linux@....linux.org.uk>,
	David Howells <dhowells@...hat.com>,
	Tony Luck <tony.luck@...el.com>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Kyle McMartin <kyle@...artin.ca>, Helge Deller <deller@....de>,
	James Bottomley <James.Bottomley@...e.de>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mundt <lethal@...ux-sh.org>,
	"David S. Miller" <davem@...emloft.net>,
	Chris Zankel <chris@...kel.net>
Subject: Re: [PATCH -mm 00/12] adds include/asm-generic/pci-dma-common.h

On Tuesday 09 February 2010, e@....ntt.co.jp wrote:
> This patchset adds include/asm-generic/pci-dma-common.h that defines
> the pci_unmap state API:
> 
> DECLARE_PCI_UNMAP_ADDR(ADDR_NAME)
> DECLARE_PCI_UNMAP_LEN(LEN_NAME)
> pci_unmap_addr(PTR, ADDR_NAME)
> pci_unmap_addr_set(PTR, ADDR_NAME, VAL)
> pci_unmap_len(PTR, LEN_NAME)
> pci_unmap_len_set(PTR, LEN_NAME, VAL)
> 
> This enables us to remove lots of the duplication in architecture
> implementations since there are only two ways to define the API.

Good stuff, moving this code to a common location is certainly
a step in the right direction.

A few general comments though:

* It seems you left out arch/cris for no good reason.
* The general tendency nowadays is to avoid new HAVE_ARCH_*
  macros and instead using either a Kconfig symbol or
  checking the presence of the macros themselves. In this case,
  the macro would always be present, so CONFIG_PCI_UNMAP
  would be reasonable.
* AFAICT, there are no architectures left doing the
  non-generic version, so the code could be moved to
  a global file in include/linux instead of include/asm-generic.
  While include/linux/pci.h is already a bit overloaded, it's
  probably the right place for this. Alternatively,
  include/linux/pci-dma.h, included from include/linux/pci.h.

> In the long term, it's better to replace the API with the generic
> device model API such as DECLARE_DMA_UNMAP_ADDR. We can map the API to
> the generic one (like dma-mapping-compat.h does). This patch also
> makes the migration process easier.

Agreed.

	Arnd
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