trouble (very slow reads -- disk or controller resets?) with Marvell 88SE92xx PCIe card

[Daniel Kahn Gillmor <dkg@fifthhorseman.net>]

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hi there--

i'm trying to boot a machine with grub-pc 2.00-19 (from debian sid), off
of two SATA disks connected to a PCIe controller.

The PCIe controller is a "​SYBA SI-PEX40064", and upon boot it announces
itself as:

Marvell 88SE92xx Adapter - BIOS Version 1.0.0.1010
PCIe x1 2.5Gbps
Mode: PassThru AHCI
Disks Information:
Port     Disk Name                            Size    Speed
S0       SATA: WDC WD2003FYYS-02W0B0          2TB     3Gb/s
S1       SATA: ST32000644NS                   2TB     3Gb/s

Both of these disks have grub installed on them, and they hang with just
the output "GRUB" on the video console.

If i boot grub 2.00-19 from a USB stick, i can get into a grub rescue
shell just fine.  But when i do "ls" to get a listing of the disks, it
pauses for over a minute after printing:

(hd0) (hd0,msdos1) (hd1) (hd2)

and before giving me back a grub> prompt.

after "insmod part_gpt" and another "ls", i get:

(hd0) (hd0,msdos1) (hd1) (hd1,gpt3) (hd1,gpt2) (hd1,gpt1) (hd2)

and then another long hang.

this makes me think that grub is causing the SATA controller to reset
itself with every disk read or something, and then grub is waiting for
it to come back to life before carrying on.

Is this something i can debug better somehow?  is there a way to tell
grub to be "gentler" with the controller or something to avoid these hangs?

	--dkg


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