From: Deepak Saxena <dsaxena@plexity.net>
To: "Amit D. Chaudhary" <amit_c@comcast.net>
Cc: linux-kernel@vger.kernel.org
Subject: Re: MAX_DMA_ADDRESS in include/asm/asm-i386/dma.h (2.6.x and 2.4.x)
Date: Fri, 16 Jul 2004 14:47:21 -0700 [thread overview]
Message-ID: <20040716214721.GA20741@plexity.net> (raw)
In-Reply-To: <40F84A87.5050403@comcast.net>
On Jul 16 2004, at 14:37, Amit D. Chaudhary was caught saying:
> While writing some DMA page gathering code, I realize that
> __get_free_page or kmalloc does not return memory more than 16 MB
> (typically around 11-12 MB even if it done right after a reboot.)
>
> Since this is for a PCI device (A Fibre channel HBA), I remembered that
> the book Linux Device Driver, edition 2 mentions that the 16 MB limit is
> for DMA with ISA devices, while PCI DMA can access upto 950 MB or so,
> using 32 bit addresses.
Using __get_free_page() or kmalloc() for device DMA'ble descriptors (I am
guessing that's what you are doing) is wrong. See Documentation/DMA-API.txt
and Documentation/DMA-mapping.txt for the proper way to do this.
~Deepak
--
Deepak Saxena - dsaxena at plexity dot net - http://www.plexity.net/
"Unlike me, many of you have accepted the situation of your imprisonment and
will die here like rotten cabbages." - Number 6
next prev parent reply other threads:[~2004-07-16 21:47 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-07-16 21:37 MAX_DMA_ADDRESS in include/asm/asm-i386/dma.h (2.6.x and 2.4.x) Amit D. Chaudhary
2004-07-16 21:47 ` Deepak Saxena [this message]
2004-07-16 22:11 ` Amit D. Chaudhary
2004-07-16 22:28 ` Deepak Saxena
2004-07-16 23:36 ` Amit D. Chaudhary
2004-08-05 19:00 ` Amit D. Chaudhary
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