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Date: Wed, 4 Feb 2004 08:05:15 -0800
From: "Randy.Dunlap" <rddunlap@osdl.org>
To: Stelian Pop <stelian@popies.net>
Cc: akpm@osdl.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] meye: correct printk of dma_addr_t
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On Wed, 4 Feb 2004 09:44:37 +0100 Stelian Pop <stelian@popies.net> wrote:

| On Tue, Feb 03, 2004 at 04:28:22PM -0800, Randy.Dunlap wrote:
| 
| > | mchip_ptable[] just contains pointers to kernel memory.  It doesn't seem
| > | appropriate to be casting these to dma_addr_t's
| > 
| > 
| > Ugh... if I am reading this correcly, what I see is that
| > mchip_table[] is mostly used for kernel pointers, like you say.
| 
| Yep. The meye driver uses 256 PAGE_SIZE buffers. The kernel virtual
| pointers to these buffers are stored in mchip_ptable[]. The
| "toc" containing the dma pointers to these buffers must be given
| to the device as a table having 256 entries, each being 32 bits in length.
| 
| In the code I used the last entry of mchip_ptable to store the toc,
| but I could as well construct a different data structure.
| 
| Anyway, the device expects a dma_addr to be 32 bits in length, so this
| will not work anyway with HIGHMEM32 (moreover, this is a driver for the
| motion eye camera which is found only in C1 Vaio Sony laptops, which
| motherboard is limited to 384 MB...).
| 
| I can see only two solutions:
| 	*) put the toc in a different, dma_addr_t[] structure, so the
| 	   driver will compile even with HIGHMEM32 (but won't work...)
| 
| 	*) exclude meye from kernel config when HIGHMEM32 is set.

  for (HIGHMEM64G=y)

| Which one do you prefer ?


Well, both.  :)

The toc of dma_addr_t's should be in its own array/structure.

Adding some comments or help text about the highmem limitation
would also be good.

--
~Randy