On Friday 19 October 2012 17:10:17 Simon Farnsworth wrote: > Mauro, Linux-Media > > I have an issue where an SAA7134-based TV capture card connected via a PCIe to > PCI bridge chip works when the GPU is kept out of RC6 state, but sometimes > "skips" updating lines of the capture when the GPU is in RC6. We've confirmed > that a CX23418 based chip doesn't have the problem, so the question is whether > the SAA7134 and the saa7134 driver are at fault, or whether it's the PCIe bus. > > This manifests as a regression, as I had no problems with kernel 3.3 (which > never enabled RC6 on the Intel GPU), but I do have problems with 3.5 and with > current Linus git master. I'm happy to try anything, > > I've attached lspci -vvxxxxx output (suitable for feeding to lspci -F) for > when the corruption is present (lspci.faulty) and when it's not > (lspci.working). The speculation is that the SAA7134 is somehow more > sensitive to the changes in timings that RC6 introduces than the CX23418, and > that someone who understands the saa7134 driver might be able to make it less > sensitive. > And timings are definitely the problem; I have a userspace provided pm_qos request asking for 0 exit latency, but I can see CPU cores entering C6. I'll take this problem to an appropriate list. There is still be a bug in the SAA7134 driver, as the card clearly wants a pm_qos request when streaming to stop the DMA latency becoming too high; this doesn't directly affect me, as my userspace always requests minimal DMA latency anyway, so consider this message as just closing down the thread for now, and as a marker for the future (if people see such corruption, the saa7134 driver needs a pm_qos request when streaming that isn't currently present). -- Simon Farnsworth Software Engineer ONELAN Ltd http://www.onelan.com
Attachment:
signature.asc
Description: This is a digitally signed message part.
