Re: [PATCH 00/15] Add runtime PM support for libsas

["chenxiang (M)" <chenxiang66@hisilicon.com>]

Hi John,


在 2021/12/14 19:52, John Garry 写道:
> On 17/11/2021 02:44, chenxiang wrote:
>> From: Xiang Chen<chenxiang66@hisilicon.com>
>>
>
> Please consider this rewrite:
>
> Currently the HiSilicon SAS controller v3 hw driver supports runtime 
> PM. However a number of corner-case bugs have been reported for this 
> feature. These include:
> a. If a directly-attached disk is removed when the host is suspended a 
> system hang may occur during resume. libsas drains events after 
> resuming the host. Draining the events causes a deadlock as we need to 
> ensure that the host is resumed for some libsas events processing, 
> however the resume process will not complete until all events are 
> processed.
> b. If a disk is attached to an expander when the host is suspended 
> then this new disk will not be detected when active again.
> c. The host controller may not resume from suspension when sending SMP 
> IOs.
> d. If a phy comes up when resuming the host controller then we may get 
> a deadlock from processing of events DISCE_DISCOVER_DOMAIN and 
> PORTE_BYTES_DMAED.
> e. Similar to d., the work of PORTE_BROADCAST_RCVD and 
> PORTE_BYTES_DMAED may deadlock.
>
> This series addresses those issues, briefly described as follows:
> a. As far as we can see, this drain is unneeded, so conditionally remove.
> b. Just insert broadcast events to revalidate the topology.
> c. and e. When processing any events from the LLD, make libsas keep 
> the host active until finished processing all work related to that 
> original event.
> d. Defer phyup event processing in case described.

Thanks for your detailed comments.
I will improve those commit message according to your suggestions.

>
>
>> Right now hisi_sas driver has already supported runtime PM, and it works
>> well on base functions. But for some exception situations, there are 
>> some
>> issues related to libsas layer:
>> - Remove a directly attached disk when sas host is suspended, a hang 
>> will
>> occur in the resume process, patch 1~2 solve the issue;
>> - Insert a new disk (for expander) during suspended, and the disk is not
>> revalidated when resuming sas host, patch 4~7 solve the issue;
>> - SMP IOs from libsas may be sending when sas host is suspended, so 
>> resume
>> sas host when sending SMP IOs in patch 9;
>> - New phyup may occur during the process of resuming controller, then 
>> work
>> of DISCE_DISCOVER_DOMAIN of a new phy and work PORTE_BYTES_DMAED of 
>> suspended
>> phy are blocked by each other, so defer works of new phys during suspend
>> in patch 10~12;
>> - Work PORTE_BROADCAST_RCVD and PORTE_BYTES_DMAED are in the same
>> workqueue, but it is possible that they are blocked by each other,
>> so keep sas host active until finished some work in patch 14.
>>
>> And patch 3 which is related to scsi/block PM is from Alan Stern
>> (https://lore.kernel.org/linux-scsi/20210714161027.GC380727@rowland.harvard.edu/) 
>>
>
>
> .
>