linux-kernel - Re: [PATCH 0/3] serial: Fix support for UPF_SPD

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Message-ID: <20220322185340.eccktabcryfanxnj@pali>
Date:   Tue, 22 Mar 2022 19:53:40 +0100
From:   Pali Rohár <pali@...nel.org>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Johan Hovold <johan@...nel.org>,
        Marek Behún <kabel@...nel.org>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/3] serial: Fix support for UPF_SPD_* flags

On Tuesday 22 March 2022 16:29:08 Andy Shevchenko wrote:
> On Mon, Mar 21, 2022 at 11:07 PM Pali Rohár <pali@...nel.org> wrote:
> >
> > Support for UPF_SPD_* flags is currently broken in more drivers for two
> > reasons. First one is that uart_update_timeout() function does not
> 
> the uart_update_timeout()
> 
> > calculate timeout for UPF_SPD_CUST flag correctly. Second reason is that
> > userspace termios structre is modified by most drivers after each
> 
> structure
> 
> ...
> 
> > (error handling was ommited for simplification)
> 
> omitted
> 
> > After calling set_active_spd_cust_baud() function SPD custom divisor
> > should be active and therefore is_spd_cust_active() should return true.
> >
> > But it is not active (cfgetospeed does not return B38400) and this patch
> > series should fix it. I have tested it with 8250 driver.
> 
> drivers
> 
> > Originally Johan Hovold reported that there may be issue with these
> > ASYNC_SPD_FLAGS in email:
> > https://lore.kernel.org/linux-serial/20211007133146.28949-1-johan@kernel.org/
> >
> >
> > Johan, Greg, could you please test these patches if there is not any
> > regression?
> 
> I'm wondering why we are still supporting this ugly hack?
> Doesn't BOTHER work for you?

Johan pointed in above mentioned patch that it would break
ASYNC_SPD_FLAGS. So I have looked at how are ASYNC_SPD_FLAGS implemented
to ensure that they would work correctly...

> I would rather expect to have this removed completely.

Well, if somebody is going to remove it, I have no objections. But I
understood that ASYNC_SPD_FLAGS should be still supported...