Re: [PATCH v2 0/3] scsi: libsas: handle linkrate change in sas_rediscover_dev

[yangxingui <yangxingui@huawei.com>]

On 2026/5/13 15:29, John Garry wrote:
> On 13/05/2026 03:16, Xingui Yang wrote:
>> When a device attached to an expander phy experiences a linkrate change
>> (e.g., due to cable reconnection or negotiation), the current code in
>> sas_rediscover_dev() treats it as "broadcast flutter" and takes no action
>> if the SAS address and device type remain unchanged.
> 
> Can sas_rediscover_dev() check the linkrate (vs expected) to understand 
> that this flutter has renegotiated the linkrate and then consider it not 
> just a flutter?

Hi, John
Theoretically, it is possible. As early as 2019, Jason attempted to 
propose the solution you mentioned. He conducted a relatively 
comprehensive assessment for flutter, including scenarios where the SAS 
address changes or the ATA ID changes. However, in actual use, such 
situations almost never occur unless there is an extremely short time 
window during which the drive is swapped or a new SATA drive is 
replaced. Because this solution is associated with other modifications 
and may have significant impacts, it has not been adopted.

https://lore.kernel.org/linux-scsi/20190130082412.9357-6-yanaijie@huawei.com/

Currently, scenarios involving changes in linkrate are relatively more 
common, and such situations can be easily reproduced by manually 
adjusting the linkrate by sysfs. Therefore, a less impactful synchronous 
update solution was adopted.

Thanks.
Xingui