Re: does sym53c8xx_2 hardware support hotplug

[Hannes Reinecke <hare@suse.de>]

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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