From: Geert Uytterhoeven <geert@linux-m68k.org>
To: "torii.ken1@fujitsu.com" <torii.ken1@fujitsu.com>
Cc: "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
"erosca@de.adit-jv.com" <erosca@de.adit-jv.com>,
"linux-serial@vger.kernel.org" <linux-serial@vger.kernel.org>,
"linux-renesas-soc@vger.kernel.org"
<linux-renesas-soc@vger.kernel.org>,
"wsa+renesas@sang-engineering.com"
<wsa+renesas@sang-engineering.com>,
"yoshihiro.shimoda.uh@renesas.com"
<yoshihiro.shimoda.uh@renesas.com>,
"uli+renesas@fpond.eu" <uli+renesas@fpond.eu>,
"george_davis@mentor.com" <george_davis@mentor.com>,
"andrew_gabbasov@mentor.com" <andrew_gabbasov@mentor.com>,
"jiada_wang@mentor.com" <jiada_wang@mentor.com>,
"yuichi.kusakabe@denso-ten.com" <yuichi.kusakabe@denso-ten.com>,
"yasano@jp.adit-jv.com" <yasano@jp.adit-jv.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"jslaby@suse.com" <jslaby@suse.com>,
"yohhei.fukui@denso-ten.com" <yohhei.fukui@denso-ten.com>,
"ashiduka@fujitsu.com" <ashiduka@fujitsu.com>,
"magnus.damm@gmail.com" <magnus.damm@gmail.com>
Subject: Re: [PATCH] serial: sh-sci: Support custom speed setting
Date: Thu, 12 Mar 2020 10:03:13 +0100 [thread overview]
Message-ID: <CAMuHMdXYPG8t=vBn6c2B=8TwbWJfFCjW8peDLgHBwW_AxpH5Hw@mail.gmail.com> (raw)
In-Reply-To: <OSBPR01MB29496E76BE5FD0C5BC56D0F0C1FD0@OSBPR01MB2949.jpnprd01.prod.outlook.com>
Hi Torii-san,
On Thu, Mar 12, 2020 at 6:10 AM torii.ken1@fujitsu.com
<torii.ken1@fujitsu.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@de.adit-jv.com> wrote:
> > > > From: Torii Kenichi <torii.ken1@jp.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@jp.fujitsu.com>
> > > > [erosca: rebase against v5.5]
> > > > Signed-off-by: Eugeniu Rosca <erosca@de.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@linux-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
next prev parent reply other threads:[~2020-03-12 9:03 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-29 16:19 [PATCH] serial: sh-sci: Support custom speed setting Eugeniu Rosca
2020-01-30 12:32 ` Geert Uytterhoeven
2020-02-10 20:57 ` Greg Kroah-Hartman
2020-02-10 21:44 ` Eugeniu Rosca
2020-02-11 8:15 ` Geert Uytterhoeven
2020-02-11 12:30 ` Greg Kroah-Hartman
2020-03-12 5:10 ` torii.ken1
2020-03-12 8:55 ` gregkh
2020-03-12 9:03 ` Geert Uytterhoeven [this message]
2020-03-12 9:44 ` ashiduka
2020-03-30 7:43 ` ashiduka
2021-07-15 21:16 ` andy
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