Re: [PATCH 01/18] arm64: dts: renesas: beacon kit: Configure programmable clocks

[Adam Ford <aford173@gmail.com>]

On Fri, Dec 18, 2020 at 7:16 AM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
>
> Hi Adam,
>
> CC Shimoda-san
>
> On Thu, Dec 17, 2020 at 12:52 PM Adam Ford <aford173@gmail.com> wrote:
> > On Thu, Dec 17, 2020 at 2:16 AM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> > > On Wed, Dec 16, 2020 at 6:03 PM Adam Ford <aford173@gmail.com> wrote:
> > > > On Wed, Dec 16, 2020 at 8:55 AM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> > > > > On Sun, Dec 13, 2020 at 7:38 PM Adam Ford <aford173@gmail.com> wrote:
> > > > > > When the board was added, clock drivers were being updated done at
> > > > > > the same time to allow the versaclock driver to properly configure
> > > > > > the modes.  Unforutnately, the updates were not applied to the board
> > >
> > > > > > --- a/arch/arm64/boot/dts/renesas/beacon-renesom-baseboard.dtsi
> > > > > > +++ b/arch/arm64/boot/dts/renesas/beacon-renesom-baseboard.dtsi
> > > > > > @@ -5,6 +5,7 @@
> > > > > >
> > > > > >  #include <dt-bindings/gpio/gpio.h>
> > > > > >  #include <dt-bindings/input/input.h>
> > > > > > +#include <dt-bindings/clk/versaclock.h>
> > > > > >
> > > > > >  / {
> > > > > >         backlight_lvds: backlight-lvds {
> > > > > > @@ -294,12 +295,12 @@ &du_out_rgb {
> > > > > >  &ehci0 {
> > > > > >         dr_mode = "otg";
> > > > > >         status = "okay";
> > > > > > -       clocks = <&cpg CPG_MOD 703>, <&cpg CPG_MOD 704>;
> > > > > > +       clocks = <&cpg CPG_MOD 703>, <&cpg CPG_MOD 704>, <&versaclock5 3>;
> > > > >
> > > > > Why this change? You said before you don't need this
> > > > > https://lore.kernel.org/linux-renesas-soc/CAHCN7xJWbP16SA-Ok-5syNnqOZAt8OFJo2_rtg5VrNVsN2-eiQ@mail.gmail.com/
> > > > >
> > > >
> > > > I had talked with the hardware guys about buy pre-programmed
> > > > versaclock chips which would have been pre-configured and pre-enabled.
> > > > I thought it was going to happen, but it didn't, so we need the
> > > > versaclock driver to enable the reference clock for the USB
> > > > controllers, ethernet controller and audio clocks.  Previously we were
> > > > manually configuring it or it was coincidentally working. Ideally,
> > > > we'd have the clock system intentionally enable/disable the clocks
> > > > when drivers are loaded/unloaded for for power management reasons.
> > >
> > > Can you tell me how exactly the Versaclock outputs are wired?
> >
> > The SoC is expecting a fixed external 50 MHz clock connected to
> > USB_EXTAL.  Instead of a fixed clock, we're using the Versaclock.
> > We're also using the Versaclock to drive the AVB TXCRefClk,
> > du_dotclkiun0 and du_dotclkin2 (also also called du_dotclkin3 on
> > RZ/G2N) instead of fixed clocks.
> >
> > > E.g. for USB, the bindings don't say anything about a third clock input,
> > > so I'd like to know where that clock is fed into USB.
> >
> > The way the driver is crafted, it can take in multiple clocks and it
> > goes through a list to enable them all, so I added the versaclock to
> > the array.  Without the versaclock reference, the clock doesn't get
> > turned on and the USB fails to operate.
>
> According to the Hardware User's Manual, USBL_EXTAL is used for USB3.0,
> while you added the clock references to the EHCI nodes.
> Are you sure EHCI is failing without this?
>
> Still, it means we need to extend the bindings/driver for
> renesas,rcar-gen3-xhci to handle USB_EXTAL.

After investigating this, it looks like the USB_EXTAL is already
referenced from the device tree and it's referenced by the USB3 Phy.
The SoC calls it usb_extal_clk.  Since the phy driver is calling
devm_clk_get() it looks like i could just redefine the clocks of
usb3_phy0 to point to the versaclock instead of usb_extal_clk.

The other option is to use a similar method I proposed for the audio
reference clock and redefine the usb_extal_clk as a fixed
fixed-factor-clock.

Do you have a preference as to which direction I go?

>
> > The DU clocks are also expecting an array, so I added the versaclock
> > to that array as well.
>
> For DU, the clock inputs are clearly defined in the bindings.
>
> > It's similar to the rationale that I'm trying to add the option clock
> > for the AVB TXC_Ref clock on the other path.  We're using the
> > versaclock there as well.  The difference is that in the case of the
> > AVB_TXCRefClk, the driver isn't expecting an array of clocks, it's
> > only expecting a single clock.  In order to enable the additional
> > clock,  I started the patch to accept the optional clock for the
> > TXCRefClk in order to get the clock system to enable the clock.
>
> Sure.
>
> > Because the Versaclock isn't programmed to automatically start, they
> > need the consumers of the clock to request and enable them.
> >
> > I admit that I'll probably need to update the bindings to add the
> > extra clocks as optional, so if you want, I can submit additional
> > patches to add these optional clocks to their respective bindings.
>
> Thanks!
>
> 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