does sym53c8xx_2 hardware support hotplug

does sym53c8xx_2 hardware support hotplug

[Mike Christie]

Hi,

Does the hardware sym53c8xx_2 works with support removing and adding 
devices?

When using sym53c8xx_2 if we find storage, remove the device using the 
sysfs/proc interface, then physically remove the device, everything goes 
well. However, if we physically plug the disk back in and try to readd 
it through the sysfs/proc scanning interfaces, it looks like 
scsi_scan.c's inquiry will time out. This causes the sym error handler 
to run, which works great and we end up doing a BUS RESET (BDR failed so 
we got escalated), and after that the inqiury is retried and we find the 
device and it works fine.

Is the inquiry timing out expected? Does the hardware even support 
hotplug? Or does it support it partially support it (support it with 
some help), and we are we supposed to be manually resetting the bus, 
with something like a sg_reset, after we have physically plug the disk 
back in?

Thanks for any info,

Mike

Re: does sym53c8xx_2 hardware support hotplug

[Hannes Reinecke]

Hi Mike,

Mike Christie wrote:
> Hi,
> 
> Does the hardware sym53c8xx_2 works with support removing and adding 
> devices?
> 
Oh. Hmm. That is tricky and complicated.

> When using sym53c8xx_2 if we find storage, remove the device using the 
> sysfs/proc interface, then physically remove the device, everything goes 
> well. However, if we physically plug the disk back in and try to readd 
> it through the sysfs/proc scanning interfaces, it looks like 
> scsi_scan.c's inquiry will time out. This causes the sym error handler 
> to run, which works great and we end up doing a BUS RESET (BDR failed so 
> we got escalated), and after that the inqiury is retried and we find the 
> device and it works fine.
> 
Yes.

> Is the inquiry timing out expected? Does the hardware even support 
> hotplug? Or does it support it partially support it (support it with 
> some help), and we are we supposed to be manually resetting the bus, 
> with something like a sg_reset, after we have physically plug the disk 
> back in?
> 
Hi, join the club.

As the saying goes: Radio Yerewan answers: in principle, yes.

The whole matter of SCSI parallel hotplugging depends strongly on
the backplane. For fun reading have a look at 

SPI-3 Annex D: Removal and insertion of SCSI devices.

It basically leaves it open to the vendor of the backplane how
much intelligence he wants to put in there.
But yes, sending a SCSI reset is listed there. It actually states
that the RST line should be asserted continuously by the initiator
during the hotplugging process.

HTH.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare@suse.de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: Markus Rex, HRB 16746 (AG Nürnberg)
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