linux-kernel - Re: [PATCH v2 1/3] Revert "USB: cdc-acm: fix rounding error in TIOCSSERIAL"

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Date:   Thu, 08 Apr 2021 15:31:49 +0200
From:   Oliver Neukum <oneukum@...e.com>
To:     Johan Hovold <johan@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        Anthony Mallet <anthony.mallet@...s.fr>, stable@...r.kernel.org
Subject: Re: [PATCH v2 1/3] Revert "USB: cdc-acm: fix rounding error in
 TIOCSSERIAL"

Am Donnerstag, den 08.04.2021, 15:16 +0200 schrieb Johan Hovold:
> This reverts commit b401f8c4f492cbf74f3f59c9141e5be3071071bb.
> 
> The offending commit claimed that trying to set the values reported back
> by TIOCGSERIAL as a regular user could result in an -EPERM error when HZ
> is 250, but that was never the case.
> 
> With HZ=250, the default 0.5 second value of close_delay is converted to
> 125 jiffies when set and is converted back to 50 centiseconds by
> TIOCGSERIAL as expected (not 12 cs as was claimed, even if that was the
> case before an earlier fix).
> 
> Comparing the internal current and new jiffies values is just fine to
> determine if the value is about to change so drop the bogus workaround
> (which was also backported to stable).
> 
> For completeness: With different default values for these parameters or
> with a HZ value not divisible by two, the lack of rounding when setting
> the default values in tty_port_init() could result in an -EPERM being
> returned, but this is hardly something we need to worry about.
> 
> Cc: Anthony Mallet <anthony.mallet@...s.fr>
> Cc: stable@...r.kernel.org
> Signed-off-by: Johan Hovold <johan@...nel.org>
Acked-by: Oliver Neukum <oneukum@...e.com>