Mikael Pettersson wrote:
I've started working on NCQ support for sata_promise, and I have a few questions regarding NCQ and libata: 1. Can I rely not seeing any non-NCQ commands while there are uncompleted NCQ commands on a port?
.. No, you cannot. So you'll have to code a .qc_defer() method to hold them off in that case. For a *really* good example, see my recently deployed mv_qc_defer() function in sata_mv.c as of linux-2.6.26-rc2.
3. Is qc->tag defined (to zero for instance) for non-NCQ commands?
.. The tag always has a valid value, NCQ or not.
4. What are these "internal commands" that map to ATA_TAG_INTERNAL? Are they NCQ or not?
.. Not NCQ, but a valid tag number regardless. libata reserves one tag for use during error-handling (EH), primarily for issing the READ_LOG_EXT_10H command to find out which NCQ command failed and what sector it failed on.
Does the existence of ATA_TAG_INTERNAL limit queue depth for NCQ?
.. Yup. Max depth is 31 instead of 32 for most devices.
5. Does dmam_alloc_coherent() give the same alignment guarantees that pci_alloc_consistent() does? That is, both CPU and bus addresses will be aligned to the smallest PAGE_SIZE order that fits the requested size.
.. In sata_mv, I ran into those same concerns, and ended up creating a couple of pools for local use by the driver. It uses dmam_pool_create() (note the extra "m" in "dmam_"), dma_pool_alloc(), and dma_pool_free(). If you just search for "_pool" in sata_mv, you'll find all of the calls (not many). The use of "dmam_pool_create()" assures that things will be cleaned up properly/automatically if the controller ever "goes away". Cheers -- To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
