Re: [PATCH v6 02/11] ARM: dts: renesas: r8a7740: Add clocks for FSI

[Geert Uytterhoeven]

Hi Phuc,

On Fri, 12 Jun 2026 at 13:08, Bui Duc Phuc <phucduc.bui@xxxxxxxxx> wrote:
> > I have one more general question.
> > arch/arm/boot/dts/renesas/r8a7740-armadillo800eva.dts configures
> > audio for FSI (fsia_pins), but does not fill in a clock-frequency
> > in fsiack_clk.  Instead, it fills in 12.288 MHz in fsibck_clk, while
> > the schematics call it FSIACK.
> > Apparently the FSIACK pin is shared with FSIBCK on R-Mobile A1, so
> > which function is used depends on pin control.  However, the DTS does
> > not perform any pin configuration for this pin?
>
> I checked the schematic in more detail.
> On sheet 12 (FSIA section), the FSIACK signal is connected to the
> WM8978 MCLK pin (pin 11).
> It is also connected to the X8 oscillator output (pin 3) through R121.
> By default, the board populates R120 (0 ohm), which routes the signal
> to R8A7740 pin K5 (FSIAOMC).
> If R120 is removed and R250 is populated instead, the signal is routed
> to pin G3 (FSIACK).

According to my schematics (RevA), R120 is not populated, but R250 is.
So the 12.288 MHz clock is fed to both the FSIACK-pin of R-Mobile A1,
and the MCLK-pin of the WM8978 codec.
Which revision of the schematics and board do you have?

> From my understanding, the default resistor configuration places FSIA
> in slave mode.
> In this configuration, FSIA receives BCLK and LRCLK from the WM8978,
> while the codec receives the 12.288 MHz MCLK from oscillator X8.
>
> This matches the current DTS configuration:
>
> simple-audio-card,codec {
>           sound-dai = <&wm8978>;
>           bitclock-master;
>           frame-master;
>           system-clock-frequency = <12288000>;
> };
>
> Therefore, I do not think it is necessary to provide a 12.288 MHz
> frequency for fsiack_clk (xcka) in the current configuration.
> If the hardware were reconfigured to operate FSIA in master mode, that
> might need to be revisited.
>
> I have considered testing the alternative resistor configuration
> (removing R120 and populating R250)
> to switch FSIA into master mode, but I have not done so due to the
> risk of damaging the board.

I haven't located R120 and R250 yet, so I don't know which
configuration my board has.

> As for the relationship between FSIACK and FSIBCK, I am not sure.
> The schematic I have does not appear to describe FSIB at all.
> The HDMI section only documents video signals and does not mention audio,
> so I do not have enough information to determine whether FSIACK and
> FSIBCK share the same pin on this board.

That information is found in the R-Mobile A1 docs (PORT11):

Table 1.3 Pin Assignment (505-Pin BGA Package)
    Ball No. / Pin Name / Multiplexed Pin Functions / GPIO
    G3 / FSIACK / FSIACK/FSIBCK / PORT11

Table 54.1 List of Multiplexed Pins
    Pin Name / Function 0 / Function 1 / Function 2
    FSIACK / PORT11 / FSIACK / FSIBCK

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

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