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Message-ID: <20200312085500.GA149342@kroah.com>
Date: Thu, 12 Mar 2020 09:55:00 +0100
From: "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
To: "torii.ken1@...itsu.com" <torii.ken1@...itsu.com>
Cc: "geert@...ux-m68k.org" <geert@...ux-m68k.org>,
"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>,
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Subject: Re: [PATCH] serial: sh-sci: Support custom speed setting
On Thu, Mar 12, 2020 at 05:10:05AM +0000, torii.ken1@...itsu.com wrote:
> Dear Greg,
>
> 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:
> > > Hi Eugeniu,
> > >
> > > 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.
Why not?
> >#include <linux/termios.h>
> >
> >int ioctl(int d, int request, ...);
>
> Do application programmers have to accept this bad code?
I do not understand what you are asking here.
greg k-h
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