linux-kernel - Re: [patch] kconfig: unify GENERIC_ISA_DMA and ISA_DMA

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Date:	Wed, 26 Jan 2011 17:22:37 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
	x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [patch] kconfig: unify GENERIC_ISA_DMA and ISA_DMA_API

On Wed, 26 Jan 2011, Russell King - ARM Linux wrote:

> Drivers should depend on ISA_DMA_API as that indicates that the ISA DMA
> API is present - in other words, when the following are available from
> an architecture/platform:
> 
> dma_spin_lock
> claim_dma_lock
> release_dma_lock
> enable_dma
> disable_dma
> clear_dma_ff
> set_dma_mode
> set_dma_page
> set_dma_addr
> set_dma_count
> get_dma_residue
> request_dma
> free_dma
> 
> GENERIC_ISA_DMA should be set by an architecture/platform when ISA_DMA_API
> has already been set -and- it wants to use kernel/dma.c.  No drivers should
> depend on GENERIC_ISA_DMA.

Very good information, thanks!  x86 wants to use kernel/dma.c since it has 
no ISA-style DMA allocator of its own, which should have tipped me off 
since they're both "def_bool y" right now (and the tons of linker failures 
when only CONFIG_GENERIC_ISA_DMA is disabled).  So what I'll do is make 
CONFIG_ISA_DMA_API select CONFIG_GENERIC_ISA_DMA for x86 -- that prevents 
all build errors for allyesconfig.  (Alpha could probably benefit from the 
same requirement.)

My end goal is to make CONFIG_GENERIC_ISA_DMA, CONFIG_ISA_DMA_API, and 
CONFIG_ZONE_DMA configurable for x86 (we've been running with that config 
for a couple years and it's a 1% savings on the kernel image).  Peter 
wanted that to be done under CONFIG_EMBEDDED after it was renamed to 
CONFIG_EXPERT so now that that's been done in 2.6.38-rc2, it should be 
well received.

Thanks Russell!
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