From: Linus Walleij <linus.walleij-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
To: Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org>
Cc: Simon Glass <sjg-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>,
"devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
<devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
U-Boot Mailing List
<u-boot-0aAXYlwwYIKGBzrmiIFOJg@public.gmane.org>,
Stephen Warren <swarren-3lzwWm7+Weoh9ZMKESR00Q@public.gmane.org>,
Stephen Warren <swarren-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>,
Joe Hershberger <joe.hershberger-acOepvfBmUk@public.gmane.org>,
Masahiro Yamada
<yamada.masahiro-uWyLwvC0a2jby3iVrkZq2A@public.gmane.org>,
Masahiro Yamada
<yamada.m-NAum8xwdG0+S7A1Ibl2khg@public.gmane.org>,
Marek Vasut <marek.vasut-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
Tom Rini <trini-OWPKS81ov/FWk0Htik3J/w@public.gmane.org>,
Albert Aribaud
<albert.u.boot-LhW3hqR2+23R7s880joybQ@public.gmane.org>,
Vikas Manocha <vikas.manocha-qxv4g6HH51o@public.gmane.org>,
Pavel Herrmann
<morpheus.ibis-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
Subject: Re: [PATCH 11/20] dm: serial: Update binding for PL01x serial UART
Date: Wed, 15 Jul 2015 12:08:05 +0200 [thread overview]
Message-ID: <CACRpkdakAVcBT8phhbFjE+mkfA0pTcHYiaL0dV4UNieH54fd+w@mail.gmail.com> (raw)
In-Reply-To: <1510062.S45KkZCs96@wuerfel>
On Wed, Jul 15, 2015 at 11:38 AM, Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org> wrote:
> The CHRP ISA binding defines that a 8250 compatible UART must have this
> property:
>
> "clock-frequency" S
>
> Standard property, encoded as with encode-int, that shall be the baud-rate
> generator's clock input frequency (in hertz).
> Typically, the clock frequency is nominally 1,843,200 Hz. Some devices
> generate the baud rate input clock by dividing a higher-frequency clock
> source that is not an exact multiple of 1,843,200 Hz, resulting in a
> small but acceptable error in the nominal clock frequency. In such cases,
> the "clock-frequency" shall report the actual nominal frequency. For
> example, if the baud rate input clock is generated by dividing a 24
> MHz clock by 13, the value of the "clock-frequency" property shall be 1846153.
Isn't that for the case where the clock frequency will never change at runtime?
The problem (I think) with many systems using PL011 is that they can
actually change the serial port clock at runtime (software controlled clock),
so providing a "clock-frequency" would imply that they cannot, and the clock
frequency is fixed to that value.
I think it's better to use boot-clock-frequency or so to indicate that a richer
OS will provide more refined clocks. For example that frequency can
typically change if the SoC changes operating point or so, though it would
be awkward to handle in the driver, admittedly and I haven't seen a
piece of code that actually go and change the UART input frequency.
Still for completion it is better for the UART to tie into the clk framework
as the OS gets up, and just providing clock-frequency seems to imply
that it need not do that or something. The semantical effect of providing both
clock-frequency = and clocks =< &..> must be clarified in any case.
Like the latter overrides the former if clock phandles can be handled by
the environment. (And this should be stated in the binding.)
Yours,
Linus Walleij
--
To unsubscribe from this list: send the line "unsubscribe devicetree" in
the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
WARNING: multiple messages have this Message-ID (diff)
From: Linus Walleij <linus.walleij@linaro.org>
To: u-boot@lists.denx.de
Subject: [U-Boot] [PATCH 11/20] dm: serial: Update binding for PL01x serial UART
Date: Wed, 15 Jul 2015 12:08:05 +0200 [thread overview]
Message-ID: <CACRpkdakAVcBT8phhbFjE+mkfA0pTcHYiaL0dV4UNieH54fd+w@mail.gmail.com> (raw)
In-Reply-To: <1510062.S45KkZCs96@wuerfel>
On Wed, Jul 15, 2015 at 11:38 AM, Arnd Bergmann <arnd@arndb.de> wrote:
> The CHRP ISA binding defines that a 8250 compatible UART must have this
> property:
>
> "clock-frequency" S
>
> Standard property, encoded as with encode-int, that shall be the baud-rate
> generator's clock input frequency (in hertz).
> Typically, the clock frequency is nominally 1,843,200 Hz. Some devices
> generate the baud rate input clock by dividing a higher-frequency clock
> source that is not an exact multiple of 1,843,200 Hz, resulting in a
> small but acceptable error in the nominal clock frequency. In such cases,
> the "clock-frequency" shall report the actual nominal frequency. For
> example, if the baud rate input clock is generated by dividing a 24
> MHz clock by 13, the value of the "clock-frequency" property shall be 1846153.
Isn't that for the case where the clock frequency will never change at runtime?
The problem (I think) with many systems using PL011 is that they can
actually change the serial port clock at runtime (software controlled clock),
so providing a "clock-frequency" would imply that they cannot, and the clock
frequency is fixed to that value.
I think it's better to use boot-clock-frequency or so to indicate that a richer
OS will provide more refined clocks. For example that frequency can
typically change if the SoC changes operating point or so, though it would
be awkward to handle in the driver, admittedly and I haven't seen a
piece of code that actually go and change the UART input frequency.
Still for completion it is better for the UART to tie into the clk framework
as the OS gets up, and just providing clock-frequency seems to imply
that it need not do that or something. The semantical effect of providing both
clock-frequency = and clocks =< &..> must be clarified in any case.
Like the latter overrides the former if clock phandles can be handled by
the environment. (And this should be stated in the binding.)
Yours,
Linus Walleij
next prev parent reply other threads:[~2015-07-15 10:08 UTC|newest]
Thread overview: 67+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-07-08 2:53 [U-Boot] [PATCH 00/20] arm: rpi: Enable USB and Ethernet driver model Raspberry Pi Simon Glass
2015-07-08 2:53 ` [U-Boot] [PATCH 01/20] dm: net: Support usbethaddr environment variable Simon Glass
2015-07-08 4:04 ` Joe Hershberger
2015-07-08 20:31 ` Simon Glass
2015-07-08 20:43 ` Joe Hershberger
2015-07-08 21:07 ` Simon Glass
2015-07-20 13:56 ` Simon Glass
2015-07-20 18:10 ` Joe Hershberger
2015-07-21 21:25 ` Simon Glass
2015-07-08 2:53 ` [U-Boot] [PATCH 02/20] dm: usb: Allow USB Ethernet whenever CONFIG_DM_ETH is not defined Simon Glass
2015-07-08 2:53 ` [U-Boot] [PATCH 03/20] dm: usb: Add an errno.h header to usb_ether.c Simon Glass
2015-07-27 23:31 ` Simon Glass
2015-07-08 2:53 ` [U-Boot] [PATCH 04/20] dm: usb: Prepare dwc2 driver for driver-model conversion Simon Glass
2015-07-27 23:31 ` Simon Glass
2015-07-08 2:53 ` [U-Boot] [PATCH 05/20] dm: usb: Add driver-model support to dwc2 Simon Glass
2015-07-27 23:32 ` Simon Glass
2015-07-08 2:53 ` [U-Boot] [PATCH 06/20] net: smsc95xx: Sort the include files Simon Glass
2015-07-27 23:32 ` Simon Glass
2015-07-08 2:53 ` [U-Boot] [PATCH 07/20] net: smsc95xx: Rename AX_RX_URB_SIZE to RX_URB_SIZE Simon Glass
2015-07-27 23:32 ` Simon Glass
2015-07-08 2:53 ` [U-Boot] [PATCH 08/20] net: smsc95xx: Correct the error numbers Simon Glass
2015-07-27 23:32 ` Simon Glass
2015-07-08 2:53 ` [U-Boot] [PATCH 09/20] net: smsc95xx: Prepare for conversion to driver model Simon Glass
2015-07-27 23:32 ` Simon Glass
2015-07-08 2:53 ` [U-Boot] [PATCH 10/20] net: smsc95xx: Add driver-model support Simon Glass
2015-07-27 23:32 ` Simon Glass
2015-07-08 2:53 ` [U-Boot] [PATCH 11/20] dm: serial: Update binding for PL01x serial UART Simon Glass
2015-07-08 22:00 ` Vikas MANOCHA
[not found] ` <1436324032-17931-12-git-send-email-sjg-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>
2015-07-15 9:00 ` Linus Walleij
2015-07-15 9:00 ` [U-Boot] " Linus Walleij
[not found] ` <CACRpkdb=t21=qpqar5VXd4mtqTWrq6MvoX1OsVgmWpkyFqhj3w-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2015-07-15 9:38 ` Arnd Bergmann
2015-07-15 9:38 ` [U-Boot] " Arnd Bergmann
2015-07-15 10:08 ` Linus Walleij [this message]
2015-07-15 10:08 ` Linus Walleij
[not found] ` <CACRpkdakAVcBT8phhbFjE+mkfA0pTcHYiaL0dV4UNieH54fd+w-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2015-07-15 10:17 ` Arnd Bergmann
2015-07-15 10:17 ` [U-Boot] " Arnd Bergmann
2015-07-16 7:41 ` Geert Uytterhoeven
2015-07-16 7:41 ` [U-Boot] " Geert Uytterhoeven
2015-10-19 7:19 ` Linus Walleij
2015-10-19 7:19 ` [U-Boot] " Linus Walleij
2015-07-08 2:53 ` [U-Boot] [PATCH 12/20] dm: Support address translation for simple-bus Simon Glass
2015-07-27 23:32 ` Simon Glass
2015-07-08 2:53 ` [U-Boot] [PATCH 13/20] arm: rpi: Define CONFIG_TFTP_TSIZE to show tftp size info Simon Glass
2015-07-08 2:53 ` [U-Boot] [PATCH 14/20] arm: rpi: Bring in kernel device tree files Simon Glass
2015-07-08 2:53 ` [U-Boot] [PATCH 15/20] arm: rpi: Device tree modifications for U-Boot Simon Glass
2015-07-08 2:53 ` [U-Boot] [PATCH 16/20] arm: rpi: Enable device tree control for Rasberry Pi Simon Glass
2015-07-08 2:53 ` [U-Boot] [PATCH 17/20] arm: rpi: Drop the UART console platform data Simon Glass
2015-07-08 2:53 ` [U-Boot] [PATCH 18/20] arm: rpi: Drop the GPIO " Simon Glass
2015-07-08 2:53 ` [U-Boot] [PATCH 19/20] arm: rpi: Move to driver model for USB Simon Glass
2015-07-08 2:53 ` [U-Boot] [PATCH 20/20] arm: rpi: Use driver model for Ethernet Simon Glass
2015-07-11 5:34 ` [U-Boot] [PATCH 00/20] arm: rpi: Enable USB and Ethernet driver model Raspberry Pi Stephen Warren
2015-07-11 14:04 ` Simon Glass
2015-07-14 4:52 ` Stephen Warren
2015-07-14 15:44 ` Simon Glass
2015-07-24 4:17 ` Stephen Warren
2015-07-24 13:44 ` Tom Rini
2015-07-28 3:10 ` Stephen Warren
2015-07-28 13:55 ` Tom Rini
2015-07-28 15:44 ` Simon Glass
2015-08-01 3:10 ` Stephen Warren
2015-08-01 3:01 ` Stephen Warren
2015-07-16 14:10 ` Pavel Machek
2015-07-20 14:25 ` Simon Glass
2015-07-24 4:20 ` Stephen Warren
2015-08-03 23:45 ` Marek Vasut
2015-08-04 0:07 ` Simon Glass
2015-08-04 0:37 ` Marek Vasut
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CACRpkdakAVcBT8phhbFjE+mkfA0pTcHYiaL0dV4UNieH54fd+w@mail.gmail.com \
--to=linus.walleij-qsej5fyqhm4dnm+yrofe0a@public.gmane.org \
--cc=albert.u.boot-LhW3hqR2+23R7s880joybQ@public.gmane.org \
--cc=arnd-r2nGTMty4D4@public.gmane.org \
--cc=devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org \
--cc=joe.hershberger-acOepvfBmUk@public.gmane.org \
--cc=marek.vasut-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org \
--cc=morpheus.ibis-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org \
--cc=sjg-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org \
--cc=swarren-3lzwWm7+Weoh9ZMKESR00Q@public.gmane.org \
--cc=swarren-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org \
--cc=trini-OWPKS81ov/FWk0Htik3J/w@public.gmane.org \
--cc=u-boot-0aAXYlwwYIKGBzrmiIFOJg@public.gmane.org \
--cc=vikas.manocha-qxv4g6HH51o@public.gmane.org \
--cc=yamada.m-NAum8xwdG0+S7A1Ibl2khg@public.gmane.org \
--cc=yamada.masahiro-uWyLwvC0a2jby3iVrkZq2A@public.gmane.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.