linux-kernel - RE: [PATCH] serial: sh-sci: Support custom speed setting

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Date:   Thu, 12 Mar 2020 09:44:13 +0000
From:   "ashiduka@...itsu.com" <ashiduka@...itsu.com>
To:     'Geert Uytterhoeven' <geert@...ux-m68k.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
CC:     "erosca@...adit-jv.com" <erosca@...adit-jv.com>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        "linux-renesas-soc@...r.kernel.org" 
        <linux-renesas-soc@...r.kernel.org>,
        "wsa+renesas@...g-engineering.com" <wsa+renesas@...g-engineering.com>,
        "yoshihiro.shimoda.uh@...esas.com" <yoshihiro.shimoda.uh@...esas.com>,
        "uli+renesas@...nd.eu" <uli+renesas@...nd.eu>,
        "george_davis@...tor.com" <george_davis@...tor.com>,
        "andrew_gabbasov@...tor.com" <andrew_gabbasov@...tor.com>,
        "jiada_wang@...tor.com" <jiada_wang@...tor.com>,
        "yuichi.kusakabe@...so-ten.com" <yuichi.kusakabe@...so-ten.com>,
        "yasano@...adit-jv.com" <yasano@...adit-jv.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "jslaby@...e.com" <jslaby@...e.com>,
        "yohhei.fukui@...so-ten.com" <yohhei.fukui@...so-ten.com>,
        "magnus.damm@...il.com" <magnus.damm@...il.com>,
        "torii.ken1@...itsu.com" <torii.ken1@...itsu.com>
Subject: RE: [PATCH] serial: sh-sci: Support custom speed setting

Dear Greg, Geert,

> I guess you mean the forward declaration of ioctrl()?
> No, they should include <sys/ioctl.h> instead.

Right.
Adding "#include <sys/ioctl.h>" to Greg's sample code causes a 
compilation error.

> > I saw the code above, I thought I wouldn't write such code normally.
> Why not?

Is it normal to declare ioctl() without "#include <sys/ioctl.h>" ?

Thanks & Best Regards,
Yuusuke Ashiduka <ashiduka@...itsu.com>
Embedded System Development Dept. Embedded System Development Div.
FUJITSU COMPUTER TECHNOLOGIES Ltd.

> -----Original Message-----
> From: Geert Uytterhoeven <geert@...ux-m68k.org>
> Sent: Thursday, March 12, 2020 6:03 PM
> To: Torii, Kenichi/鳥居 健一 <torii.ken1@...itsu.com>
> Cc: gregkh@...uxfoundation.org; erosca@...adit-jv.com;
> linux-serial@...r.kernel.org; linux-renesas-soc@...r.kernel.org;
> wsa+renesas@...g-engineering.com;
> yoshihiro.shimoda.uh@...esas.com; uli+renesas@...nd.eu;
> george_davis@...tor.com; andrew_gabbasov@...tor.com;
> jiada_wang@...tor.com; yuichi.kusakabe@...so-ten.com;
> yasano@...adit-jv.com; linux-kernel@...r.kernel.org;
> jslaby@...e.com; yohhei.fukui@...so-ten.com; Ashizuka, Yuusuke/
> 芦塚 雄介 <ashiduka@...itsu.com>; magnus.damm@...il.com
> Subject: Re: [PATCH] serial: sh-sci: Support custom speed setting
> 
> Hi Torii-san,
> 
> On Thu, Mar 12, 2020 at 6:10 AM torii.ken1@...itsu.com
> <torii.ken1@...itsu.com> wrote:
> > On Tue, 11 Feb 2020 05:57:35 +0900,
> > Greg Kroah-Hartman wrote:
> > > On Thu, Jan 30, 2020 at 01:32:50PM +0100, Geert Uytterhoeven
> wrote:
> > > > On Wed, Jan 29, 2020 at 5:20 PM Eugeniu Rosca
> <erosca@...adit-jv.com> wrote:
> > > > > From: Torii Kenichi <torii.ken1@...fujitsu.com>
> > > > >
> > > > > This patch is necessary to use BT module and XM module with
> DENSO TEN
> > > > > development board.
> > > > >
> > > > > This patch supports ASYNC_SPD_CUST flag by ioctl(TIOCSSERIAL),
> enables
> > > > > custom speed setting with setserial(1).
> > > > >
> > > > > The custom speed is calculated from uartclk and
> custom_divisor.
> > > > > If custom_divisor is zero, custom speed setting is invalid.
> > > > >
> > > > > Signed-off-by: Torii Kenichi <torii.ken1@...fujitsu.com>
> > > > > [erosca: rebase against v5.5]
> > > > > Signed-off-by: Eugeniu Rosca <erosca@...adit-jv.com>
> > > >
> > > > Thanks for your patch!
> > > >
> > > > While this seems to work fine[*], I have a few
> comments/questions:
> > > >   1. This feature seems to be deprecated:
> > > >
> > > >          sh-sci e6e68000.serial: setserial sets custom speed
> on
> > > > ttySC1. This is deprecated.
> > > >
> > > >   2. As the wanted speed is specified as a divider, the resulting
> speed
> > > >      may be off, cfr. the example for 57600 below.
> > > >      Note that the SCIF device has multiple clock inputs, and
> can do
> > > >      57600 perfectly if the right crystal has been fitted.
> > > >
> > > >  3. What to do with "[PATCH/RFC] serial: sh-sci: Update uartclk
> based
> > > >      on selected clock"
> (https://patchwork.kernel.org/patch/11103703/)?
> > > >      Combined with this, things become pretty complicated and
> > > >      unpredictable, as uartclk now always reflect the frequency
> of the
> > > >      last used base clock, which was the optimal one for the
> previously
> > > >      used speed....
> > > >
> > > > I think it would be easier if we just had an API to specify
> a raw speed.
> > > > Perhaps that already exists?
> > >
> > > Yes, see:
> > >       http://www.panix.com/~grante/arbitrary-baud.c
> >
> > I saw the code above, I thought I wouldn't write such code normally.
> >
> > >#include <linux/termios.h>
> > >
> > >int ioctl(int d, int request, ...);
> >
> > Do application programmers have to accept this bad code?
> 
> I guess you mean the forward declaration of ioctrl()?
> No, they should include <sys/ioctl.h> instead.
> 
> Gr{oetje,eeting}s,
> 
>                         Geert
> 
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 --
> geert@...ux-m68k.org
> 
> In personal conversations with technical people, I call myself a
> hacker. But
> when I'm talking to journalists I just say "programmer" or something
> like that.
>                                 -- Linus Torvalds