linux-kernel - Re: [PATCH 1/4] dma: document dma_{un}map_{single|sg}

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Date:	Thu, 31 Jan 2008 19:07:51 -0800
From:	akepner@....com
To:	Grant Grundler <grundler@...isc-linux.org>
Cc:	Tony Luck <tony.luck@...el.com>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Jes Sorensen <jes@....com>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	Roland Dreier <rdreier@...co.com>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	David Miller <davem@...emloft.net>,
	Muli Ben-Yehuda <muli@...ibm.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] dma: document dma_{un}map_{single|sg}_attrs() interface

On Thu, Jan 31, 2008 at 03:38:48PM -0700, Grant Grundler wrote:

Thanks for looking through this.

I'll send an updated patchset that addresses your comments 
as soon as I can - probably around Monday.

> ...
> > +struct dma_attrs encapsulates a set of "dma attributes". For the 
> > +definition of struct dma_attrs see linux/dma-attrs.h. 
> 
> Because all architectures will share the set of attrs definitions,
> would it be reasonable to document the intent of each attr?
> 
> Two reasons for doing this:
> 1) people reading the driver code should understand WHY the dma attr was added.
> 2) other arch maintainers need to know in order to implement the same attr
>    for their shiny new toys.
> 
> 
> > +The interpretation of dma attributes is architecture-specific. 
> 
> This statement is really important....but:
> Could we add a reference to arch documentation for each attr?
> 
> ie something public (doesn't have to be in linux source tree)
> which explains the subtlies of how that DMA attr actually works.
> 
> Having worked on HP chipsets for 10+ years, I know releasing
> original HW docs is often not possible. I'm not asking for the
> impossible. Please don't flame me for that. But if the company
> is willing to publish the existance of a feature, a paragraph or
> two would be good marketing too. Maybe just include comments in
> the arch/ code that implements the feature and reference those
> comments in DMA-API.txt.
> ....

OK, I can certainly add an explanation of the attribute that
I'm worried about. 

I think there's a reference to this behavior in our driver 
porting guide - I can add a pointer to that, too. 

This might also address your point above about documenting 
each attribute - let me know once the next patch is out.

-- 
Arthur

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