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

[John Garry]

On 13/05/2026 09:14, yangxingui wrote:
> 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://urldefense.com/v3/__https://lore.kernel.org/linux- 
> scsi/20190130082412.9357-6-yanaijie@xxxxxxxxxx/__;!!ACWV5N9M2RV99hQ! 
> K7CIIOxMVXErIMxcZlvm10YX3EVqp0rhSbh_ARyqnaFDmtaqqJtoLTJQui0- 
> Ox_URh97f8oyREG8htBVo2aC3Ew$
> 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.

What Jason did was to check if same device for flutter, which is not 
really the same thing as what you want.

I just don't like these special case callbacks which you propose, as 
they seem fragile and too specialized.

Is it possible to just check the linkrate and mark the device as gone 
and rediscover when this flutter occurs occurs?