the4hoffmans@xxxxxxxxxxxxx wrote:
Update: We got Fedora 2.6.25-14 build running. It recognizes our card. It identifies our device but at some point after that we die. Using an analyzer we found that the problem is due to a buffer alignment issue. Our card is a prototype and currently under development. It currently only supports memory buffers that are quadword aligned. We are dying because we get a buffer for a subsequent identify command that is on a dword boundary. That is the problem we need to solve next. We know we need to change our hardware and we will do that. However, is there a way during driver init to specify quadword buffer alignment so we can continue our testing with Linux?
Not easily, no :/ The entirety of SATA, both devices, the protocol, and controllers, are all very 32-bit-centric. Given that each SATA FIS is one or more dwords, this fundamental feature propagates through everything touched by SATA: Linux kernel drivers, controller interfaces, etc.
I would be surprised if standard filesystem I/O (via bio's) was unaligned... but all the ATA commands we use for control, various internal [and often controller-specific] data structures that are DMA-mapped and directly accessed are usually found on 32-bit boundaries, but nothing more than that.
Avoiding commands outside the READ DMA / WRITE DMA realm may help you limp along... if you want to hack things up to speed up local development, I would turn on libata DEBUG and VERBOSE_DEBUG, follow the trace until you find the failing (non-aligned) command, and try to omit that from the probing process. The main non-data operation during probing we really care about is IDENTIFY [PACKET] DEVICE, and that /should/ be aligned at a minimum on a quadword boundary, if I'm not mistaken.
Also, avoid ATAPI devices and testing ATAPI, as you will _definitely_ not be getting quadword alignment there.
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