fb_write unaligned writes

[James Hogan <james@albanarts.com>]

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Hi,

I came across a problem in fb_write (drivers/video/fbmem.c) which doesn't make 
any effort to avoid unaligned writes. It copies up to a page at a time from 
userspace into a buffer, then fb_writel's as much as possible from the buffer 
into the framebuffer, then fb_writeb's any remaining bytes. However on 
architectures which don't perform unaligned writes this can cause a bus error 
or silently fail when it tries to fb_writel to an unaligned framebuffer 
position.

My question is how best should this be fixed? I know I could avoid writing 
more than 3 bytes to an unaligned framebuffer offset, but the standard write 
syscall should be able to handle this, and Documentation/unaligned-memory-
access.txt makes it clear that unaligned accesses are to be avoided and with 
good reason.

Is it possible to just copy_from_user straight into the framebuffer, or should 
I define an fb_memcpy to go with the other definitions around line 925 of 
include/linux/fb.h, or something else?

Thanks
James

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