Hi Tejun,
On 11/27/2017 01:19 PM, Tejun Heo wrote:
Hello, David.
On Tue, Nov 14, 2017 at 04:17:25PM -0600, 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.
Can you please explain the scenario with more details?
Yes, in this particular case (I had a second reporter, but,
they didn't respond to my questions), when disconnecting
the drive, the error handler limits the speed to 1.5 Gpps
by setting bit 4 of the control register. And when the drive
is reconnected the status register show a link speed of 3Gbps,
even though before hot unplug it was running a 6Gbps.
/* Mask off all speeds higher than or equal to the current
- * one. Force 1.5Gbps if current SPD is not available.
+ * one. At this point if current SPD is not available and we
+ * previously recorded the link speed from the Status register,
+ * the driver has already masked off the highest bit so mask
+ * should already be set to 1 or 0. Otherwise, we should
+ * not force 1.5Gbps on a link where we have not previously
+ * recorded speed from Status register, just return in this case.
*/
if (spd > 1)
mask &= (1 << (spd - 1)) - 1;
else
- mask &= 1;
+ return -EINVAL;
I get that the current behavior might not be ideal in certain
scenarios but the above seems weird, especially given the we have
link->sata_spd for cases where we can't access the spd value.
Yes, but link->sata_spd is initialized to 0, and the only time the
driver records "link->sata_spd" from the status register is in
ata_eh_reset(). And on hot unplug, the driver sets the mask to 1
dropping the link from 6 to 1.5Gbps. And, if the driver doesn't
downgrade the link speed by writing to the control register, the link
comes back at 6Gbps on hot plug. It maybe particular controller/configs
behave differently since it is not always reproducible.
Thanks,
David
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