netdev - Re: [PATCH net-next RFC 00/13] Add devlink reload level option

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Message-ID: <7fd63d16-f9fa-9d55-0b30-fe190d0fb1cb@mellanox.com>
Date:   Mon, 3 Aug 2020 16:52:02 +0300
From:   Moshe Shemesh <moshe@...lanox.com>
To:     Vasundhara Volam <vasundhara-v.volam@...adcom.com>
Cc:     Jacob Keller <jacob.e.keller@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jiri Pirko <jiri@...lanox.com>,
        Netdev <netdev@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next RFC 00/13] Add devlink reload level option


On 8/3/2020 3:47 PM, Vasundhara Volam wrote:
> On Mon, Aug 3, 2020 at 5:47 PM Moshe Shemesh <moshe@...lanox.com> wrote:
>>
>> On 8/3/2020 1:24 PM, Vasundhara Volam wrote:
>>> On Tue, Jul 28, 2020 at 10:13 PM Jacob Keller <jacob.e.keller@...el.com> wrote:
>>>>
>>>> On 7/27/2020 10:25 PM, Vasundhara Volam wrote:
>>>>> On Mon, Jul 27, 2020 at 4:36 PM Moshe Shemesh <moshe@...lanox.com> wrote:
>>>>>> Introduce new option on devlink reload API to enable the user to select the
>>>>>> reload level required. Complete support for all levels in mlx5.
>>>>>> The following reload levels are supported:
>>>>>>     driver: Driver entities re-instantiation only.
>>>>>>     fw_reset: Firmware reset and driver entities re-instantiation.
>>>>> The Name is a little confusing. I think it should be renamed to
>>>>> fw_live_reset (in which both firmware and driver entities are
>>>>> re-instantiated).  For only fw_reset, the driver should not undergo
>>>>> reset (it requires a driver reload for firmware to undergo reset).
>>>>>
>>>> So, I think the differentiation here is that "live_patch" doesn't reset
>>>> anything.
>>> This seems similar to flashing the firmware and does not reset anything.
>>
>> The live patch is activating fw change without reset.
>>
>> It is not suitable for any fw change but fw gaps which don't require reset.
>>
>> I can query the fw to check if the pending image change is suitable or
>> require fw reset.
> Okay.
>>>>>>     fw_live_patch: Firmware live patching only.
>>>>> This level is not clear. Is this similar to flashing??
>>>>>
>>>>> Also I have a basic query. The reload command is split into
>>>>> reload_up/reload_down handlers (Please correct me if this behaviour is
>>>>> changed with this patchset). What if the vendor specific driver does
>>>>> not support up/down and needs only a single handler to fire a firmware
>>>>> reset or firmware live reset command?
>>>> In the "reload_down" handler, they would trigger the appropriate reset,
>>>> and quiesce anything that needs to be done. Then on reload up, it would
>>>> restore and bring up anything quiesced in the first stage.
>>> Yes, I got the "reload_down" and "reload_up". Similar to the device
>>> "remove" and "re-probe" respectively.
>>>
>>> But our requirement is a similar "ethtool reset" command, where
>>> ethtool calls a single callback in driver and driver just sends a
>>> firmware command for doing the reset. Once firmware receives the
>>> command, it will initiate the reset of driver and firmware entities
>>> asynchronously.
>>
>> It is similar to mlx5 case here for fw_reset. The driver triggers the fw
>> command to reset and all PFs drivers gets events to handle and do
>> re-initialization.  To fit it to the devlink reload_down and reload_up,
>> I wait for the event handler to complete and it stops at driver unload
>> to have the driver up by devlink reload_up. See patch 8 in this patchset.
>>
> Yes, I see reload_down is triggering the reset. In our driver, after
> triggering the reset through a firmware command, reset is done in
> another context as the driver initiates the reset only after receiving
> an ASYNC event from the firmware.


Same here.

>
> Probably, we have to use reload_down() to send firmware command to
> trigger reset and do nothing in reload_up.
I had that in previous version, but its wrong to use devlink reload this 
way, so I added wait with timeout for the event handling to complete 
before unload_down function ends. See mlx5_fw_wait_fw_reset_done(). Also 
the event handler stops before load back to have that done by devlink 
reload_up.
>   And returning from reload
> does not mean that reset is complete as it is done in another context
> and the driver notifies the health reporter once the reset is
> complete. devlink framework may have to allow drivers to implement
> reload_down only to look more clean or call reload_up only if the
> driver notifies the devlink once reset is completed from another
> context. Please suggest.