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Date:   Tue, 18 Aug 2020 12:58:24 +0200
From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     Badhri Jagan Sridharan <badhri@google.com>
Cc:     Guenter Roeck <linux@roeck-us.net>,
        Heikki Krogerus <heikki.krogerus@linux.intel.com>,
        linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org,
        Hans de Goede <hdegoede@redhat.com>
Subject: Re: [PATCH v5] usb: typec: tcpm: Migrate workqueue to RT priority
 for processing events
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References: <20200731065830.3744049-1-badhri@google.com>
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On Thu, Jul 30, 2020 at 11:58:30PM -0700, Badhri Jagan Sridharan wrote:
> "tReceiverResponse 15 ms Section 6.6.2
> The receiver of a Message requiring a response Shall respond
> within tReceiverResponse in order to ensure that the
> sender’s SenderResponseTimer does not expire."
> 
> When the cpu complex is busy running other lower priority
> work items, TCPM's work queue sometimes does not get scheduled
> on time to meet the above requirement from the spec.
> Moving to kthread_work apis to run with real time priority.
> Just lower than the default threaded irq priority,
> MAX_USER_RT_PRIO/2 + 1. (Higher number implies lower priority).
> 
> Further, as observed in 1ff688209e2e, moving to hrtimers to
> overcome scheduling latency while scheduling the delayed work.
> 
> TCPM has three work streams:
> 1. tcpm_state_machine
> 2. vdm_state_machine
> 3. event_work
> 
> tcpm_state_machine and vdm_state_machine both schedule work in
> future i.e. delayed. Hence each of them have a corresponding
> hrtimer, tcpm_state_machine_timer & vdm_state_machine_timer.
> 
> When work is queued right away kthread_queue_work is used.
> Else, the relevant timer is programmed and made to queue
> the kthread_work upon timer expiry.
> 
> kthread_create_worker only creates one kthread worker thread,
> hence single threadedness of workqueue is retained.
> 
> Signed-off-by: Badhri Jagan Sridharan <badhri@google.com>
> Reviewed-by: Guenter Roeck <linux@roeck-us.net>
> Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
> ---

With this patch applied I get the following build breakage:

ERROR: modpost: "sched_setscheduler" [drivers/usb/typec/tcpm/tcpm.ko] undefined!

Please fix up and resend against 5.9-rc1.

thanks,

greg k-h