Tejun Heo wrote:
ATAPI devices come with plethora of bugs and many ATA controllers have trouble dealing with odd byte DMA transfers. The problem is currently somewhat masked by not allowing DMA transfers if the transfer size isn't aligned to 16 bytes plus partial masking in problematic LLDs. This masking is taken verbatim from IDE and is far from perfection. There's no fundamental explanation why this should be sufficient and there are ATAPI devices which don't work with the IDE driver. In addition, this mixture of PIO and DMA commands reduces test coverage which is already insufficient considering the crazy number of ATAPI devices out in the wild. Also, these misc ATAPI commands usually transfer small amount of data and are used infrequently. There isn't much to be gained from using DMA. Combined with the fact that another OS which is probably the only one that most ATAPI device vendors test against uses PIO for these commands, it's much wiser to use PIO for these commands and concentrate debugging efforts on getting PIO right for misc commands and DMA for bulk transfer commands. Private command type / transfer length filtering in sata_promise, pata_it821x and pata_pdc2027x are removed as core layer filtering is more conservative. Signed-off-by: Tejun Heo <htejun@xxxxxxxxx>
The other patches were OK, but I'm still not happy about "punishing the good guys"
- 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
