Williams, Dan J wrote: > Channel switching is problematic for some dmaengine drivers as the > architecture precludes separating the ->prep from ->submit. In these > cases the driver can select ASYNC_TX_DISABLE_CHANNEL_SWITCH to modify > the async_tx allocator to only return channels that support all of the > required asynchronous operations. > > For example MD_RAID456=y selects support for asynchronous xor, xor > validate, pq, pq validate, and memcpy. When > ASYNC_TX_DISABLE_CHANNEL_SWITCH=y any channel with all these > capabilities is marked DMA_ASYNC_TX allowing async_tx_find_channel() to > quickly locate compatible channels with the guarantee that dependency > chains will remain on one channel. When > ASYNC_TX_DISABLE_CHANNEL_SWITCH=n async_tx_find_channel() may select > channels that lead to operation chains that need to cross channel > boundaries using the async_tx channel switch capability. > > Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx> > --- Signed-off-by: Maciej Sosnowski <maciej.sosnowski@xxxxxxxxx> with one question: > + /* note: this only matters in the > + * CONFIG_ASYNC_TX_DISABLE_CHANNEL_SWITCH=y case > + */ > + if (device_has_all_tx_types(device)) > + dma_cap_set(DMA_ASYNC_TX, device->cap_mask); Why not to put this part plus device_has_all_tx_types() into #ifdef CONFIG_ASYNC_TX_DISABLE_CHANNEL_SWITCH then? Thanks, Maciej-- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
