netdev - [PATCH net] ice: make writes to /dev/gnssX synchronous

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Message-ID: <MW4PR11MB580019D13E9E393B1993D89086899@MW4PR11MB5800.namprd11.prod.outlook.com>
Date:   Wed, 29 Mar 2023 09:58:54 +0000
From:   "Kolacinski, Karol" <karol.kolacinski@...el.com>
To:     mschmidt <mschmidt@...hat.com>,
        "Nguyen, Anthony L" <anthony.l.nguyen@...el.com>,
        "Kubalewski, Arkadiusz" <arkadiusz.kubalewski@...el.com>
CC:     poros <poros@...hat.com>,
        "intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: [PATCH net] ice: make writes to /dev/gnssX synchronous

Hi Michal,

Thank you for your patch - we really like it but need some further
investigation and deep testing.

>  - The GNSS write_raw operation is supposed to be synchronous[1][2].

Synchronous writes were present in first design but we experienced
multiple issues due to the asynchronous nature of our SW -> I2C
interface.
In the case of this patch, I experience terminal and gpsd hang and errors.
We need to check it on more different systems.

>  - There is no upper bound on the number of pending writes.
>    Userspace can submit writes much faster than the driver can process,
>    consuming unlimited amounts of kernel memory.
> 
>  - The possibility of waiting for a very long time to flush the write
>    work when doing rmmod, softlockups.

This will happen anyway, because I2C writes are using AQ. This is done
in a loop, AQ write can sleep etc.

Kind regards,
Karol Kolacinski