Messages in this thread | | | Date | Sun, 26 Jul 2009 15:26:55 -0600 | From | Jonathan Corbet <> | Subject | Re: Should I use kmap or kmap_atomic to map user pages that will be written in a loop ? |
| |
On Sat, 25 Jul 2009 23:41:47 +0200 Laurent Pinchart <laurent.pinchart@skynet.be> wrote:
> Pages will be written to from the kernel in USB interrupt context. I can then > either kmap_atomic() pages before copying data and kunmap_atomic() them right > after, or kmap() them once at the beginning of the video stream and keep them > mapped until the end.
Video buffers can be big, and the streaming interface requires at least two of them. That's a lot of kmap'd pages. It seems to me that kmap_atomic() is the way to go for something like this.
But, then, these are user-space buffers, and you're seemingly buffering the data through kernel space buffers first? It seems like using copy_to_user() in a workqueue (or a threaded interrupt handler) might be a more straightforward way to go, unless I'm missing something.
jon
| |