Re: How to map high memory for block io

[Russell King <rmk+lkml@arm.linux.org.uk>]

On Fri, Jan 27, 2006 at 01:14:15PM +0100, Pierre Ossman wrote:
> Russell, would having a "highmem not supported" flag in the host
> structure be an acceptable solution? mmc_block could then use that to
> tell the block layer that bounce buffers are needed. As for other,
> future, users they would have to take care not to give those drivers
> highmem sg lists.

The mmc_block layer only tells the block layer what the driver told it.

> The current buggy code, was modeled after another MMC driver (mmci). So
> I suspect there might be more occurrences like this. Perhaps an audit
> should be added as a janitor project?

I don't see what the problem is.  A sg entry is a list of struct page
pointers, an offset, and a size.  As such, it can't describe a transfer
which crosses a page because such a structure does not imply that one
struct page follows another struct page.

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:  2.6 Serial core