linux-kernel - Re: [RFC PATCH] usb: hcd: complete URBs in threaded-IRQ context instead of tasklet

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Date:   Thu, 8 Mar 2018 10:57:39 +0100
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Mauro Carvalho Chehab <mchehab@...pensource.com>
Cc:     Frederic Weisbecker <frederic@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Alan Stern <stern@...land.harvard.edu>,
        linux-usb@...r.kernel.org
Subject: Re: [RFC PATCH] usb: hcd: complete URBs in threaded-IRQ context
 instead of tasklet

On 2018-02-27 14:39:34 [-0300], Mauro Carvalho Chehab wrote:
> Hi Sebastian,
Hi Mauro,

> Sorry for taking some time to test it, has been busy those days...
:)

> Anyway, I tested it today. Didn't work. It keep losing data.

Okay, this was unexpected. What I learned from the thread is that you
use the dwc2 controller and once upgrade to a kernel which completes the
URBs in BH context then you starting losing data from your DVB-s USB
device. And it was assumed that this is because BH/ksoftirq is getting
"paused" if it is running for too long. If that is the case then a
revert of "let us complete the URB in BH context" should get it working
again. Is that so?

diff --git a/drivers/usb/dwc2/hcd.c b/drivers/usb/dwc2/hcd.c
--- a/drivers/usb/dwc2/hcd.c
+++ b/drivers/usb/dwc2/hcd.c
@@ -4287,7 +4287,9 @@ void dwc2_host_complete(struct dwc2_hsotg *hsotg, struct dwc2_qtd *qtd,
 	kfree(qtd->urb);
 	qtd->urb = NULL;
 
+	spin_unlock(&hsotg->lock);
 	usb_hcd_giveback_urb(dwc2_hsotg_to_hcd(hsotg), urb, status);
+	spin_lock(&hsotg->lock);
 }
 
 /*
@@ -4968,7 +4970,7 @@ static struct hc_driver dwc2_hc_driver = {
 	.hcd_priv_size = sizeof(struct wrapper_priv_data),
 
 	.irq = _dwc2_hcd_irq,
-	.flags = HCD_MEMORY | HCD_USB2 | HCD_BH,
+	.flags = HCD_MEMORY | HCD_USB2,
 
 	.start = _dwc2_hcd_start,
 	.stop = _dwc2_hcd_stop,
-- 
2.16.2


> Regards,

Sebastian