Re: [Qemu-devel] [PATCH 1/6] ahci: move PIO Setup FIS before transfer, fix it for ATAPI commands

[Paolo Bonzini]

On 02/06/2018 03:22, John Snow wrote:
> - Status: Should be the status register after receiving the H2D Register
>   update FIS, but prior to the data transfer, I think. "New value of the
>   Status register of the Command Block for initiation of host data
>   transfer."
>   I think this is being set correctly after this patch.
> 
> - Error: "Contains the new value of the Error register of the Command
>   Block at the conclusion of all subsequent Data to Device frames."
> 
>   This is why we were sending out post-hoc PIO Setup FIS frames before,
>   how would I know what the error register *will* be...? What?

You don't, I guess.  Zero?

> - LBA: Presumably unimportant for the purposes of receiving a command
>   PACKET, as we won't be writing it to disk, but a buffer. The values
>   can be reported dutifully.
> 
> - Device: Just report the register value dutifully.
> 
> - Count: Likely just relays 0, as the H2D REG FIS should have updated
>   that to zero as part of the PACKET command, as per ATA8 ACS3 7.21.3.
>   In any case, just report the register value dutifully.
> 
> - E_Status: "Contains the new value of the Status register of the
>   Command Block at the conclusion of the subsequent Data FIS."
> 
>   Again, how would I know...?
> 
> - Transfer Count: Should be 12, as per what we specified in 0xA1
>   IDENTIFY PACKET DEVICE, see core.c line 234. Your patch gets this
>   correct, as we'll actually report the PIO FIS for the packet itself.
> 
> 
> What this patch does do, though, is change the context of the Status,
> Error and E_Status registers to something different. Everything else
> should be the same, but I'd feel better about taking this patch if I
> understood what exactly this FIS packet was supposed to convey, but I don't.

At least Status and Transfer Count are correct after this patch. :/

Paolo