On Wednesday 20 October 2010, Dave Young wrote: > be curious, why can't just fix the lock_kernel logic of i810? Fixing > is too hard? > > Find a i810 hardware should be possible, even if the hardware does not > support SMP, can't we test the fix with preemption? Yes, that should work too. My usual approach for removing the BKL without having the hardware myself was to make locking stricter, i.e. replace the BKL with a new spinlock or mutex. This way all the code would still be serialized and if I did something wrong, lockdep would complain about it, but there would be no risk of silent data corruption. In case of i810, locking across DRM is rather complicated and there is no way of doing this without making changes to other DRM code. In fact, the only critical section that is actually protected by the BKL are the few lines in i810_mmap_buffers. They look like they might not even need the BKL to start with and we can just remove it even on SMP/PREEMPT, except for perhaps the assignment to buf_priv->currently_mapped. Someone who understands more about the driver than I do can probably figure this out easily, but I couldn't come up with a way that doesn't risk breaking in corner cases. Arnd -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
