Re: [PATCH 0/2] libata: hotplug link speed

[Tejun Heo <tj@kernel.org>]

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.

Thanks.

-- 
tejun