linux-kernel - Re: Driver-level memory management

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Message-ID: <20070812050409.GC13496@linux-sh.org>
Date:	Sun, 12 Aug 2007 14:04:09 +0900
From:	Paul Mundt <lethal@...ux-sh.org>
To:	Michael Bourgeous <sts.nitrogen@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Driver-level memory management

On Sat, Aug 11, 2007 at 09:14:00PM -0600, Michael Bourgeous wrote:
> I'm working on a driver for older HDTV cards based on the TL880 chip.
> These cards typically have 16MB of their own memory, which is
> available to me over the PCI bus.  Various functions of the card
> require me to manage this memory, allocating and freeing chunks of it
> as necessary.  I can easily include my own allocation and management
> code, but I'm sure this is a problem that has been solved before.
> I've found two interesting sets of functions, the kmem_cache_* and
> mempool_* functions, but neither does quite what I'm looking for.  So,
> in a sentence, my question is this: Does the kernel provide memory
> pool functions that would allow me to call the appropriate equivalent
> of kmalloc/kfree, using the card's memory as the pool instead of
> actually allocating physical or virtual memory?
> 
Many platforms have similar requirements for DMA, both in terms of bounce
buffers and consistent allocations. If you're looking at this
specifically for DMA, then things like dma_declare_coherent_memory() and
the corresponding alloc/free routines that go along with it will do what
you need. If you require something more generalized, you can still
abstract what you need fairly trivially.

There are a few examples of bitmap based region management in the kernel
you can look at. arch/i386/kernel/pci-dma.c implements the aforementioned
DMA ops, and arch/sh/kernel/cpu/sh4/sq.c does something similar, albeit
with a larger address range (64MB). A simple bitmap approach from one or
the other should work fine for your 16MB case.
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