Hi Tejun,
On 10/21/2017 11:53 AM, Tejun Heo wrote:
Hello, David.
On Thu, Oct 19, 2017 at 01:30:34PM -0500, David Milburn wrote:
During hotplug, it is possible for 6Gbps link speed to
be limited all the way down to 1.5 Gbps which may lead
to a slower link speed when drive is re-connected.
This behavior has been seen on a Intel Lewisburg SATA
controller (8086:a1d2) with HGST HUH728080ALE600 drive
where SATA link speed was limited to 1.5 Gbps and
when re-connected the link came up 3.0 Gbps. ata_dev_init
initializes link->spd to 0, but, the 0001 patch will
reset it once the link comes online. The 0002 patch will
allow the error handler to reset link->spd only if the
link is online; otherwise, it will always get set to 0.
This patch set was retested on above configuration and
showed the hotplugged link to come back online at max
speed (6Gbps). I did not see the downgrade when testing
on Intel C600/X79, but retested patched linux-4.14-rc5
kernel and didn't see any side effects from these
changes. Also, successfully retested hotplug on port
multiplier 3Gbps link.
While the problem seems valid, I'm not sure the patches are in the
right direction. Isn't the root cause the decision we're making in
sata_down_spd_limit() where the code is explicitly choosing 1.5Gbps if
spd information isn't available? It'd make more sense to make better
decisions there rather than faking the information going into them.
Ok, I will take a closer look at sata_down_spd_limit().
Thanks,
David
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