Date:   Wed, 5 Aug 2020 09:32:07 +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 8/4/2020 1:13 PM, Vasundhara Volam wrote:
> On Mon, Aug 3, 2020 at 7:23 PM Moshe Shemesh <moshe@...lanox.com> wrote:
>>
>> 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.
> But "devlink dev reload" will be invoked by the user only on a single
> dev handler and all function drivers will be re-instantiated upon the
> ASYNC event. reload_down and reload_up are invoked only the function
> which the user invoked.
>
> Take an example of a 2-port (PF0 and PF1) adapter on a single host and
> with some VFs loaded on the device. User invokes "devlink dev reload"
> on PF0, ASYNC event is received on 2 PFs and VFs for reset. All the
> function drivers will be re-instantiated including PF0.
>
> If we wait for some time in reload_down() of PF0 and then call load in
> reload_up(), this code will be different from other function drivers.


I see your point here, but the user run devlink reload command on one 
PF, in this case of fw-reset it will influence other PFs, but that's a 
result of the fw-reset, the user if asked for params change or namespace 
change that was for this PF.

>>>    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.

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