On Thu, Apr 26, 2007 at 09:41:22AM -0400, David Acker wrote: > Here is a quote from Russell that describes what I believe is the main > problem: > http://www-gatago.com/linux/kernel/15457063.html > " > Has e100 actually been fixed to use the PCI DMA API correctly yet? > Looking at it, it doesn't look like it, so until it does, eepro100 > is the far better bet for platforms needing working DMA API. > > What I'm talking about is e100's apparant belief that it can modify > rfd's in the receive ring on a non-cache coherent architecture and > expect the data around it to remain unaffected (see e100_rx_alloc_skb): > > struct rfd { > u16 status; > u16 command; > u32 link; > u32 rbd; > u16 actual_size; > u16 size; > }; > > it touches command and link. This means that the whole rfd plus > maybe the following or preceding 16 bytes get loaded into a cache > line (assuming cache lines of 32 bytes), and that data written > out again at sync. However, it does this on what seems to be an > active receive chain. > > So, both the CPU _and_ the device own the same data. Which is a > violation of the DMA API. > " > > I think that the S-bit patch fixes it because the hardware spins on the > s-bit instead of using the packet. With just the el-bit, the hardware > tries to use the same cache line that the software is updating. > > Can someone from Intel let us know if I understand the hardware's > handling of the S and EL bits? If my interpretation is correct, can the > s-bit patch be applied? It seems like the correct way to lock out the > hardware while a packet is being updated. I have not seen a reason > given not to apply the patch.
This is all a while ago now, but wasn't the e100 S-bit patch originally written by Intel people in response to the very same quote by Russell King that you've quoted above? The S-bit patch should probably just be applied, IMHO. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
