linux-kernel - Re: [RFC] MMIO accessors & barriers documentation

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Message-Id: <632CC6D1-65AB-448F-B680-06E350AFD432@kernel.crashing.org>
Date:	Tue, 12 Sep 2006 17:32:13 +0200
From:	Segher Boessenkool <segher@...nel.crashing.org>
To:	Jeff Garzik <jgarzik@...ox.com>
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Linux Kernel list <linux-kernel@...r.kernel.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	"David S. Miller" <davem@...emloft.net>,
	Paul Mackerras <paulus@...ba.org>,
	Linus Torvalds <torvalds@...l.org>,
	Andrew Morton <akpm@...l.org>
Subject: Re: [RFC] MMIO accessors & barriers documentation

> prepare_to_read_dma_memory() is the operation that an ethernet  
> driver's RX code wants.  And this is _completely_ unrelated to  
> MMIO.  It just wants to make sure that the device and host are  
> looking at the same data.  Often this involves polling a DMA  
> descriptor (or index, stored inside DMA-able memory) looking for  
> changes.
>
> flush_my_writes_to_dma_memory() is the operation that an ethernet  
> driver's TX code wants, to precede either an MMIO "poke" or any  
> other non-MMIO operation where the driver needs to be certain that  
> the write is visible to the PCI device, should the PCI device  
> desire to read that area of memory.

Because those are the operations, those should be the actual
function names, too (well, prefixed with pci_).  Architectures
can implement them whatever way is appropriate, or perhaps default
to some ultra-strong semantics if they prefer;  driver writers
should not have to know about the underlying mechanics (like why
we need which barriers).


Segher

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