linux-kernel - Re: [PATCH v3 3/6] serial: core: fix sanitizing check for RTS settings

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Message-ID: <fe473887-3aa0-9a32-53d2-a39ce5247ccb@linux.intel.com>
Date:   Mon, 16 Oct 2023 13:05:37 +0300 (EEST)
From:   Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To:     Lino Sanfilippo <LinoSanfilippo@....de>
cc:     Lino Sanfilippo <l.sanfilippo@...bus.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>, shawnguo@...nel.org,
        s.hauer@...gutronix.de, mcoquelin.stm32@...il.com,
        alexandre.torgue@...s.st.com, cniedermaier@...electronics.com,
        LKML <linux-kernel@...r.kernel.org>,
        linux-serial <linux-serial@...r.kernel.org>,
        Lukas Wunner <lukas@...ner.de>, p.rosenberger@...bus.com,
        stable@...r.kernel.org
Subject: Re: [PATCH v3 3/6] serial: core: fix sanitizing check for RTS
 settings

On Sat, 14 Oct 2023, Lino Sanfilippo wrote:
> On 13.10.23 12:24, Ilpo Järvinen wrote:
> > On Thu, 12 Oct 2023, Lino Sanfilippo wrote:
> >> On 12.10.23 15:10, Ilpo Järvinen wrote:
> >>> On Wed, 11 Oct 2023, Lino Sanfilippo wrote:
> >>>
> >>>> Among other things uart_sanitize_serial_rs485() tests the sanity of the RTS
> >>>> settings in a RS485 configuration that has been passed by userspace.
> >>>> If RTS-on-send and RTS-after-send are both set or unset the configuration
> >>>> is adjusted and RTS-after-send is disabled and RTS-on-send enabled.
> >>>>
> >>>> This however makes only sense if both RTS modes are actually supported by
> >>>> the driver.
> >>>>
> >>>> With commit be2e2cb1d281 ("serial: Sanitize rs485_struct") the code does
> >>>> take the driver support into account but only checks if one of both RTS
> >>>> modes are supported. This may lead to the errorneous result of RTS-on-send
> >>>> being set even if only RTS-after-send is supported.
> >>>>
> >>>> Fix this by changing the implemented logic: First clear all unsupported
> >>>> flags in the RS485 configuration, then adjust an invalid RTS setting by
> >>>> taking into account which RTS mode is supported.
> >>>>
> >>>> Cc: stable@...r.kernel.org
> >>>> Fixes: be2e2cb1d281 ("serial: Sanitize rs485_struct")
> >>>> Signed-off-by: Lino Sanfilippo <l.sanfilippo@...bus.com>
> >>>> ---
> >>>>  drivers/tty/serial/serial_core.c | 28 ++++++++++++++++++----------
> >>>>  1 file changed, 18 insertions(+), 10 deletions(-)
> >>>>
> >>>> diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
> >>>> index 697c36dc7ec8..f4feebf8200f 100644
> >>>> --- a/drivers/tty/serial/serial_core.c
> >>>> +++ b/drivers/tty/serial/serial_core.c
> >>>> @@ -1370,19 +1370,27 @@ static void uart_sanitize_serial_rs485(struct uart_port *port, struct serial_rs4
> >>>>               return;
> >>>>       }
> >>>>
> >>>> +     rs485->flags &= supported_flags;
> >>>> +
> >>>>       /* Pick sane settings if the user hasn't */
> >>>> -     if ((supported_flags & (SER_RS485_RTS_ON_SEND|SER_RS485_RTS_AFTER_SEND)) &&
> >>>> -         !(rs485->flags & SER_RS485_RTS_ON_SEND) ==
> >>>> +     if (!(rs485->flags & SER_RS485_RTS_ON_SEND) ==
> >>>>           !(rs485->flags & SER_RS485_RTS_AFTER_SEND)) {
> >>>> -             dev_warn_ratelimited(port->dev,
> >>>> -                     "%s (%d): invalid RTS setting, using RTS_ON_SEND instead\n",
> >>>> -                     port->name, port->line);
> >>>> -             rs485->flags |= SER_RS485_RTS_ON_SEND;
> >>>> -             rs485->flags &= ~SER_RS485_RTS_AFTER_SEND;
> >>>> -             supported_flags |= SER_RS485_RTS_ON_SEND|SER_RS485_RTS_AFTER_SEND;
> >>>> -     }
> >>>> +             if (supported_flags & SER_RS485_RTS_ON_SEND) {
> >>>> +                     rs485->flags |= SER_RS485_RTS_ON_SEND;
> >>>> +                     rs485->flags &= ~SER_RS485_RTS_AFTER_SEND;
> >>>>
> >>>> -     rs485->flags &= supported_flags;
> >>>> +                     dev_warn_ratelimited(port->dev,
> >>>> +                             "%s (%d): invalid RTS setting, using RTS_ON_SEND instead\n",
> >>>> +                             port->name, port->line);
> >>>> +             } else {
> >>>> +                     rs485->flags |= SER_RS485_RTS_AFTER_SEND;
> >>>> +                     rs485->flags &= ~SER_RS485_RTS_ON_SEND;
> >>>
> >>> So if neither of the flags is supported, what will happen? You might want
> >>> add if after that else?
> >>>
> >>
> >> I would consider this a bug in the driver, as at least one of both modes
> >> has to be supported. If the driver does not have at least one of both flags
> >> set in rs485_supported.flags we could print a warning though. Would you prefer that?
> >
> > 8250_exar.c needs to fixed then?
> I was taking these as things one can
> > "configure" even if when there's support only for a one of them there's
> > not that much to configure. As there was neither in 8250_exar's code, I
> > didn't add either flag.
> 
> > But I suppose your interpretation of those flag makes more sense.
> 
> IMHO this is consistent with what we have in uart_get_rs485_mode(). This function
> ensures that we have at least one RTS mode set (with default to RTS_ON_SEND). So
> concerning 8250_exar.c, I think it should be fixed (havent noticed the missing
> RTS mode though until you mentioned it). Would you like to provide a fix for this
> or shall I include one into the next version of this series?

Just create that fix yourself thank you and include it into your series, 
I'm busy with other stuff currently.


-- 
 i.