Re: [patch/rfc 2.6.22-rc7] usb/dma doc updates
David Brownell <[email protected]>
| Newsgroups | gmane.linux.usb.devel |
|---|---|
| Message-ID | <[email protected]> |
On Monday 02 July 2007, Oliver Neukum wrote: > Am Montag, 2. Juli 2007 schrieb David Brownell: > > + Most drivers should *NOT* be using these primitives. On most systems > > + the memory returned will be uncached, so it's a bit more expensive to > > + access than what kmalloc() returns. > > This is somewhat hard to understand. Should that be two separate paragraphs then? "don't", then "this is probably going to be uncached." ? > If we use this memory as > a real working space it makes sense. But if we do a memcpy() into > the buffer, why do we care? The data has to hit RAM for DMA to work. > So why not do the work at once, at least in the write path? > > We are as an advantage sure to get memory we can do DMA to. The reason not to use those operations is that most drivers have no need for dma-coherent memory. The normal stuff does just fine. - Dave ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/ _______________________________________________ [email protected] To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel