* Péter Ujfalusi <peter.ujfalusi@xxxxxx> [111104 02:00]: > On Thursday 03 November 2011 14:27:56 Tony Lindgren wrote: > > > > Should these tests be done only after the errata re-read for both > > src and dst patches? Otherwise the errata will not be handled? > > Yes that might be a good idea. > I was trying to locate the original errata description for DMA_ERRATA_3_3, but > it does not exist, or at least I can not find it. This only been mentioned in > the kernel's comment. Seems it got added with commit d3c9be2f. > I'm not sure when this DMA_ERRATA_3_3 would have been in force. My guess would > be that if someone wants to read the src/dst position right after the channel > is disabled, but what would we expect it to return when the channel has been > disabled? No idea.. Or read it after stopping it? > I mean what is the reasonable src/dst for a disabled channel? 0 is as good as > any other number, probably the programmed start of the DMA transfer would be > my best bet. > I think the errata description for DMA_ERRATA_3_3 is not correct, and it is in > fact to handle the case I'm also handling: Before the first DMA request the > CDAC is 0 (since we configured it to be), the CSAC contains _something_ (most > of the time 0, but can be random number). > In some situation re-reading the src/dst position will give enough time to > receive the first DMA request, which will update CDAC/CSAC registers. Yeah could be since the handling is just an immediate re-read of the register.. > What do you think? Probably the safest thing to do is move your check after the re-read test in case there's more to the ERRATA_3_3. Regards, Tony -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
