linux-kernel - Re: [PATCH 4.19 024/113] tty: serial: msm_serial: avoid system lockup condition

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Date:   Thu, 15 Aug 2019 09:07:39 +0200
From:   Pavel Machek <pavel@...x.de>
To:     Jorge Ramirez <jorge.ramirez-ortiz@...aro.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 4.19 024/113] tty: serial: msm_serial: avoid system
 lockup condition

Hi!

> >> [ Upstream commit ba3684f99f1b25d2a30b6956d02d339d7acb9799 ]

> > Should it use something like 5000*udelay(100), instead, as that has
> > chance to result in closer-to-500msec wait?
> 
> the half a second timeout didnt mean to be accurate but a worst case
> scenario...I am not sure accuracy matters.

Well, I'd be afraid that it would wait 5 seconds, not half a
second. udelay(1) may be very inaccurate.

> >>  	while (!(msm_read(port, UART_SR) & UART_SR_TX_EMPTY)) {
> >>  		if (msm_read(port, UART_ISR) & UART_ISR_TX_READY)
> >>  			break;
> >>  		udelay(1);
> >> +		if (!timeout--)
> >> +			break;
> >>  	}
> >>  	msm_write(port, UART_CR_CMD_RESET_TX_READY, UART_CR);
> >>  }
> > 
> > Plus, should it do some kind of dev_err() to let users know that
> > something went very wrong with their serial?
> 
> I did consider this but then I thought that 1/2 second without
> interrupts on the core should not go unnoticed. But I might be wrong.

Well, maybe it will be noticed, but user will have no idea what caused
it.

								Pavel
-- 
DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany

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