On 8/8/2013 5:19 PM, Sekhar Nori wrote: > On Monday 05 August 2013 09:44 PM, Joel Fernandes wrote: >> We certainly don't want error conditions to be cleared any other >> place but the EDMA error handler, as this will make us 'forget' >> about missed events we might need to know errors have occurred. >> >> This fixes a race condition where the EMR was being cleared >> by the transfer completion interrupt handler. >> >> Basically, what was happening was: >> >> Missed event >> | >> | >> V >> SG1-SG2-SG3-Null >> \ >> \__TC Interrupt (Almost same time as ARM is executing >> TC interrupt handler, an event got missed and also forgotten >> by clearing the EMR). >> >> This causes the following problems: >> >> 1. >> If error interrupt is also pending and TC interrupt clears the EMR >> by calling edma_stop as has been observed in the edma_callback function, >> the ARM will execute the error interrupt even though the EMR is clear. >> As a result, the dma_ccerr_handler returns IRQ_NONE. If this happens >> enough number of times, IRQ subsystem disables the interrupt thinking >> its spurious which makes error handler never execute again. >> >> 2. >> Also even if error handler doesn't return IRQ_NONE, the removing of EMR >> removes the knowledge about which channel had a missed event, and thus >> a manual trigger on such channels cannot be performed. >> >> The EMR is ultimately being cleared by the Error interrupt handler >> once it is handled so we remove code that does it in edma_stop and >> allow it to happen there. >> >> Signed-off-by: Joel Fernandes <joelf@xxxxxx> > > Queuing this for v3.11 fixes. While committing, I changed the headline > to remove capitalization and made it more readable by removing register > level details. The new headline is: > > ARM: edma: don't clear missed events in edma_stop() Forgot to ask, should this be tagged for stable? IOW, how serious is this race in current kernel (without the entire series applied)? I have never observed it myself - so please provide details how easy/difficult it is to hit this condition. Thanks, Sekhar -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
