Re: [PATCH 01/25] serial: sh-sci: Update DT binding documentation for external clock input

From	Geert Uytterhoeven <geert@linux-m68k.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH 01/25] serial: sh-sci: Update DT binding documentation for external clock input
Date	2015-11-20 09:10 +0100
Message-ID	<qwOVB-4AF-39@gated-at.bofh.it> (permalink)
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Hi Laurent,

On Thu, Nov 19, 2015 at 10:17 PM, Laurent Pinchart
<laurent.pinchart@ideasonboard.com> wrote:
> On Thursday 19 November 2015 21:39:50 Geert Uytterhoeven wrote:
>> On Thu, Nov 19, 2015 at 9:27 PM, Laurent Pinchart wrote:
>> > On Thursday 19 November 2015 22:19:14 Laurent Pinchart wrote:
>> >> On Thursday 19 November 2015 19:38:40 Geert Uytterhoeven wrote:
>> >> > Amend the DT bindings to include the optional external clock on
>> >> > (H)SCI(F) and some SCIFA, where this pin can serve as a clock input,
>> >> > depending on board wiring.
>> >> >
>> >> > --- a/Documentation/devicetree/bindings/serial/renesas,sci-serial.txt
>> >> > +++ b/Documentation/devicetree/bindings/serial/renesas,sci-serial.txt
>> >> >
>> >> > @@ -43,6 +43,9 @@ Required properties:
>> >> >    - clocks: Must contain a phandle and clock-specifier pair for each
>> >> >      entry in clock-names.
>> >> >    - clock-names: Must contain "fck" for the SCIx UART functional
>> >> >    clock.
>> >> > +    On (H)SCI(F) and some SCIFA, an additional clock may be specified:
>> >>
>> >> Could you list the SCIFA variants that support external clocks ?
>> >>
>> >> > +      - "hsck" for the optional external clock input (on HSCIF),
>> >> > +      - "sck" for the optional external clock input (on other
>> >> > variants).
>> >
>> > Additionally, those clocks are used as inputs to the baud rate generator
>> > for external clocks, as the ones listed in patch 02/25 in this series.
>> > I'd merge the two patches and clarify the wording.
>>
>> "SCK" predates the BRG, it even exists on SCI in H8/300.
>>
>> That SCK is used as input to the BRG is just an artefact of how the BRG was
>> added to the SCIF. The BRG is just muxed with the existing SCK to form a
>> clock input, which is muxed with the BRR clock through the SCSCR.CKEx bits.
>> And the BRG itself can choose between SCIF_CLK and INT_CLK.
>>
>> Hence that's why I split it in two parts.
>
> It makes sense with the explanation.
>
> I think some of the patches should be clarified to mention BRG-EC (or whatever
> you want to call it) instead of just BRG, as otherwise it's very easy to
> confuse the two BRGs. The (H)SCK clock is an input to the internal BRG, while
> the SCIF_CLK and INT_CLK are inputs to the BRG-EC. Without clarification the
> DT bindings and the code can be hard to understand.

The (H)SCK clock is not an input to the internal BRG: it's used directly as the
sampling clock.

I'll add more clarification...

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
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Thread

[PATCH 00/25] serial: sh-sci: Add external clock and BRG Support Geert Uytterhoeven <geert+renesas@glider.be> - 2015-11-19 19:50 +0100
  [PATCH 22/25] ARM: shmobile: koelsch dts: Enable SCIF_CLK frequency and pins Geert Uytterhoeven <geert+renesas@glider.be> - 2015-11-19 19:50 +0100
  [PATCH 16/25] serial: sh-sci: Correct SCIF type on RZ/A1H Geert Uytterhoeven <geert+renesas@glider.be> - 2015-11-19 19:50 +0100
  [PATCH 20/25] serial: sh-sci: Add support for optional BRG on (H)SCIF Geert Uytterhoeven <geert+renesas@glider.be> - 2015-11-19 19:50 +0100
  [PATCH 18/25] serial: sh-sci: Prepare for multiple clocks and baud rate generators Geert Uytterhoeven <geert+renesas@glider.be> - 2015-11-19 19:50 +0100
    Re: [PATCH 18/25] serial: sh-sci: Prepare for multiple clocks and baud rate generators Laurent Pinchart <laurent.pinchart@ideasonboard.com> - 2015-11-19 22:10 +0100
      Re: [PATCH 18/25] serial: sh-sci: Prepare for multiple clocks and  baud rate generators Geert Uytterhoeven <geert@linux-m68k.org> - 2015-11-20 09:00 +0100
        Re: [PATCH 18/25] serial: sh-sci: Prepare for multiple clocks and baud rate generators Laurent Pinchart <laurent.pinchart@ideasonboard.com> - 2015-11-20 15:50 +0100
          Re: [PATCH 18/25] serial: sh-sci: Prepare for multiple clocks and  baud rate generators Geert Uytterhoeven <geert@linux-m68k.org> - 2015-11-20 16:20 +0100
            Re: [PATCH 18/25] serial: sh-sci: Prepare for multiple clocks and baud rate generators Laurent Pinchart <laurent.pinchart@ideasonboard.com> - 2015-11-20 16:40 +0100
  [PATCH 05/25] serial: sh-sci: Drop unused frame_len parameter for sci_baud_calc_hscif() Geert Uytterhoeven <geert+renesas@glider.be> - 2015-11-19 19:50 +0100
  [PATCH 23/25] arm64: renesas: r8a7795 dtsi: Add BRG support for (H)SCIF Geert Uytterhoeven <geert+renesas@glider.be> - 2015-11-19 19:50 +0100
    Re: [PATCH 23/25] arm64: renesas: r8a7795 dtsi: Add BRG support for (H)SCIF Laurent Pinchart <laurent.pinchart@ideasonboard.com> - 2015-11-19 22:10 +0100
      Re: [PATCH 23/25] arm64: renesas: r8a7795 dtsi: Add BRG support for (H)SCIF Geert Uytterhoeven <geert@linux-m68k.org> - 2015-11-20 09:20 +0100
  [PATCH 02/25] serial: sh-sci: Update DT binding documentation for BRG support Geert Uytterhoeven <geert+renesas@glider.be> - 2015-11-19 19:50 +0100
    Re: [PATCH 02/25] serial: sh-sci: Update DT binding documentation for BRG support Laurent Pinchart <laurent.pinchart@ideasonboard.com> - 2015-11-19 21:30 +0100
      Re: [PATCH 02/25] serial: sh-sci: Update DT binding documentation for  BRG support Geert Uytterhoeven <geert@linux-m68k.org> - 2015-11-19 21:50 +0100
        Re: [PATCH 02/25] serial: sh-sci: Update DT binding documentation for BRG support Laurent Pinchart <laurent.pinchart@ideasonboard.com> - 2015-11-19 22:20 +0100
          Re: [PATCH 02/25] serial: sh-sci: Update DT binding documentation for  BRG support Geert Uytterhoeven <geert@linux-m68k.org> - 2015-11-20 09:00 +0100
  [PATCH 04/25] serial: sh-sci: Grammar s/Get ... for/Get ... from/ Geert Uytterhoeven <geert+renesas@glider.be> - 2015-11-19 19:50 +0100
  [PATCH 17/25] serial: sh-sci: Correct SCIF type on R-Car for BRG Geert Uytterhoeven <geert+renesas@glider.be> - 2015-11-19 19:50 +0100
    Re: [PATCH 17/25] serial: sh-sci: Correct SCIF type on R-Car for BRG Laurent Pinchart <laurent.pinchart@ideasonboard.com> - 2015-11-19 22:00 +0100
      Re: [PATCH 17/25] serial: sh-sci: Correct SCIF type on R-Car for BRG Geert Uytterhoeven <geert@linux-m68k.org> - 2015-11-20 08:50 +0100
        Re: [PATCH 17/25] serial: sh-sci: Correct SCIF type on R-Car for BRG Laurent Pinchart <laurent.pinchart@ideasonboard.com> - 2015-11-20 16:00 +0100
          Re: [PATCH 17/25] serial: sh-sci: Correct SCIF type on R-Car for BRG Laurent Pinchart <laurent.pinchart@ideasonboard.com> - 2015-11-20 16:40 +0100
          Re: [PATCH 17/25] serial: sh-sci: Correct SCIF type on R-Car for BRG Geert Uytterhoeven <geert@linux-m68k.org> - 2015-11-20 16:40 +0100
  [PATCH 06/25] serial: sh-sci: Don't overwrite clock selection in serial_console_write() Geert Uytterhoeven <geert+renesas@glider.be> - 2015-11-19 19:50 +0100
  [PATCH 13/25] serial: sh-sci: Take into account sampling rate for max baud rate Geert Uytterhoeven <geert+renesas@glider.be> - 2015-11-19 19:50 +0100
  [PATCH 21/25] ARM: shmobile: r8a7791 dtsi: Add BRG support for (H)SCIF Geert Uytterhoeven <geert+renesas@glider.be> - 2015-11-19 19:50 +0100
  [PATCH 14/25] serial: sh-sci: Add BRG register definitions Geert Uytterhoeven <geert+renesas@glider.be> - 2015-11-19 19:50 +0100
    Re: [PATCH 14/25] serial: sh-sci: Add BRG register definitions Laurent Pinchart <laurent.pinchart@ideasonboard.com> - 2015-11-19 21:50 +0100
  [PATCH 07/25] serial: sh-sci: Convert from clk_get() to devm_clk_get() Geert Uytterhoeven <geert+renesas@glider.be> - 2015-11-19 19:50 +0100
    Re: [PATCH 07/25] serial: sh-sci: Convert from clk_get() to devm_clk_get() Laurent Pinchart <laurent.pinchart@ideasonboard.com> - 2015-11-19 21:40 +0100
  [PATCH 01/25] serial: sh-sci: Update DT binding documentation for external clock input Geert Uytterhoeven <geert+renesas@glider.be> - 2015-11-19 19:50 +0100
    Re: [PATCH 01/25] serial: sh-sci: Update DT binding documentation for external clock input Laurent Pinchart <laurent.pinchart@ideasonboard.com> - 2015-11-19 21:20 +0100
      Re: [PATCH 01/25] serial: sh-sci: Update DT binding documentation for external clock input Laurent Pinchart <laurent.pinchart@ideasonboard.com> - 2015-11-19 21:30 +0100
        Re: [PATCH 01/25] serial: sh-sci: Update DT binding documentation for  external clock input Geert Uytterhoeven <geert@linux-m68k.org> - 2015-11-19 21:50 +0100
          Re: [PATCH 01/25] serial: sh-sci: Update DT binding documentation for external clock input Laurent Pinchart <laurent.pinchart@ideasonboard.com> - 2015-11-19 22:20 +0100
            Re: [PATCH 01/25] serial: sh-sci: Update DT binding documentation for  external clock input Geert Uytterhoeven <geert@linux-m68k.org> - 2015-11-20 09:10 +0100
      Re: [PATCH 01/25] serial: sh-sci: Update DT binding documentation for  external clock input Geert Uytterhoeven <geert@linux-m68k.org> - 2015-11-19 21:40 +0100
  [PATCH 03/25] serial: sh-sci: Drop useless check for zero sampling_rate Geert Uytterhoeven <geert+renesas@glider.be> - 2015-11-19 19:50 +0100
  [PATCH 24/25] arm64: renesas: salvator-x dts: Enable SCIF_CLK frequency and pins Geert Uytterhoeven <geert+renesas@glider.be> - 2015-11-19 19:50 +0100
  [PATCH 19/25] serial: sh-sci: Add support for optional external (H)SCK input Geert Uytterhoeven <geert+renesas@glider.be> - 2015-11-19 19:50 +0100
  [PATCH 11/25] serial: sh-sci: Avoid calculating the receive margin for HSCIF Geert Uytterhoeven <geert+renesas@glider.be> - 2015-11-19 20:00 +0100
  [PATCH 12/25] serial: sh-sci: Merge sci_scbrr_calc() and sci_baud_calc_hscif() Geert Uytterhoeven <geert+renesas@glider.be> - 2015-11-19 20:00 +0100
  [PATCH 10/25] serial: sh-sci: Improve bit rate error calculation for HSCIF Geert Uytterhoeven <geert+renesas@glider.be> - 2015-11-19 20:00 +0100
  Re: [PATCH 00/25] serial: sh-sci: Add external clock and BRG Support Laurent Pinchart <laurent.pinchart@ideasonboard.com> - 2015-11-19 22:10 +0100
    Re: [PATCH 00/25] serial: sh-sci: Add external clock and BRG Support Geert Uytterhoeven <geert@linux-m68k.org> - 2015-11-20 09:30 +0100
      Re: [PATCH 00/25] serial: sh-sci: Add external clock and BRG Support Laurent Pinchart <laurent.pinchart@ideasonboard.com> - 2015-11-20 10:00 +0100
        Re: [PATCH 00/25] serial: sh-sci: Add external clock and BRG Support Geert Uytterhoeven <geert@linux-m68k.org> - 2015-11-20 10:10 +0100
          Re: [PATCH 00/25] serial: sh-sci: Add external clock and BRG Support Laurent Pinchart <laurent.pinchart@ideasonboard.com> - 2015-11-20 16:00 +0100
            Re: [PATCH 00/25] serial: sh-sci: Add external clock and BRG Support Geert Uytterhoeven <geert@linux-m68k.org> - 2015-11-20 16:40 +0100
  Re: [PATCH 00/25] serial: sh-sci: Add external clock and BRG Support Geert Uytterhoeven <geert@linux-m68k.org> - 2015-11-20 10:10 +0100
  Re: [PATCH 00/25] serial: sh-sci: Add external clock and BRG Support Simon Horman <horms@verge.net.au> - 2015-11-24 03:50 +0100

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