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Subject: Re: [PATCH v2 3/3] USB: cdc-acm: fix TIOCGSERIAL implementation
From:   Oliver Neukum <oneukum@suse.com>
To:     Johan Hovold <johan@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org
Date:   Thu, 08 Apr 2021 15:33:04 +0200
In-Reply-To: <20210408131602.27956-4-johan@kernel.org>
References: <20210408131602.27956-1-johan@kernel.org>
         <20210408131602.27956-4-johan@kernel.org>
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Am Donnerstag, den 08.04.2021, 15:16 +0200 schrieb Johan Hovold:
> TIOCSSERIAL is a horrid, underspecified, legacy interface which for most
> serial devices is only useful for setting the close_delay and
> closing_wait parameters.
> 
> The xmit_fifo_size parameter could be used to set the hardware transmit
> fifo size of a legacy UART when it could not be detected, but the
> interface is limited to eight bits and should be left unset when it is
> not used.
> 
> Similarly, baud_base could be used to set the UART base clock when it
> could not be detected, but might as well be left unset when it is not
> known (which is the case for CDC).
> 
> Fix the cdc-acm TIOCGSERIAL implementation by dropping its custom
> interpretation of the unused xmit_fifo_size and baud_base fields, which
> overflowed the former with the URB buffer size and set the latter to the
> current line speed. Also return the port line number, which is the only
> other value used besides the close parameters.
> 
> Note that the current line speed can still be retrieved through the
> standard termios interfaces.
> 
> Fixes: 18c75720e667 ("USB: allow users to run setserial with cdc-acm")
> Signed-off-by: Johan Hovold <johan@kernel.org>
Acked-by: Oliver Neukum <oneukum@suse.com>