Re: [RFC PATCH net-next 2/8] ethtool: Add ability to reset transceiver modules

On Tue, 10 Aug 2021 16:05:07 +0300 Ido Schimmel wrote:

quoted

Again, i'm wondering, why is user space doing the reset? Can you think
of any other piece of hardware where Linux relies on user space
performing a reset before the kernel can properly use it?

How long does a reset take? Table 10-1 says the reset pulse must be
10uS and table 10-2 says the reset should not take longer than
2000ms.  

Takes about 1.5ms to get an ACK on the reset request and another few
seconds to ensure module is in a valid operational state (will remove
RTNL in next version).

Hm. RTNL-lock-less ethtool ops are a little concerning. The devlink
locking was much complicated by the unclear locking rules. Can we keep
ethtool simple and put this functionality in a different API or make
the reset async?

quoted

So maybe reset it on ifup if it is in a bad state?  

We can have multiple ports (split) using the same module and in CMIS
each data path is controlled by a different state machine. Given the
complexity of these modules and possible faults, it is possible to
imagine a situation in which a few ports are fine and the rest are
unable to obtain a carrier.

Resetting the module on ifup of swp1s0 is not intuitive and it shouldn't
affect other split ports (e.g., swp1s1). With the dedicated reset
command we have the ability to enforce all the required restrictions
from the start instead of changing the behavior of existing commands.

Sounds similar to what ethtool --reset was trying to address (upper
16 bits). Could we reuse that? Whether its a SFP or other part of the
port being reset may not be entirely important to the user, so perhaps
it's not a bad idea to abstract that away and stick to "reset levels"?