Le 09/07/2010 13:53, Albert ARIBAUD a écrit :
Le 09/07/2010 13:11, Prafulla Wadaskar a écrit :
You can use volatile qualifier for the variables in DMA specific code instead of modifying structures, Try to use memory barrier or something like that- Some ref : http://gcc.gnu.org/ml/gcc/2003-04/msg01180.html may be someone c-expert on the list can suggest better
Seems we've followed the same line of reasoning. :)
I'll look into forcing a sequence point without resorting to asm.
Found it. arch/arm/include/asm/system.h provides isb() which expands to an asm statement acting as a sequence point. Inserting an isb() right before starting DMA ensures that all writes to the descriptor are emitted before setting the TQC register for DMA, so that should work.
Shouldn't I send out the isb() fix as a separate patch? After all, it is a fix for a bug (uncontrolled sequencing) which is present for kirkwood even though we were lucky enough that it did not bite so far.
Amicalement,