linux-kernel - Re: [RFC] ravb: Add support for optional txc

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Date:   Mon, 28 Dec 2020 07:49:39 -0600
From:   Adam Ford <aford173@...il.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Adam Ford-BE <aford@...conembedded.com>,
        Charles Stevens <charles.stevens@...icpd.com>,
        Sergei Shtylyov <sergei.shtylyov@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        netdev <netdev@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] ravb: Add support for optional txc_refclk

On Mon, Dec 14, 2020 at 4:05 AM Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
>
> Hi Adam,
>
> On Sun, Dec 13, 2020 at 5:18 PM Adam Ford <aford173@...il.com> wrote:
> > The SoC expects the txv_refclk is provided, but if it is provided
> > by a programmable clock, there needs to be a way to get and enable
> > this clock to operate.  It needs to be optional since it's only
> > necessary for those with programmable clocks.
> >
> > Signed-off-by: Adam Ford <aford173@...il.com>
>
> Thanks for your patch!
>
> > --- a/drivers/net/ethernet/renesas/ravb.h
> > +++ b/drivers/net/ethernet/renesas/ravb.h
> > @@ -994,6 +994,7 @@ struct ravb_private {
> >         struct platform_device *pdev;
> >         void __iomem *addr;
> >         struct clk *clk;
> > +       struct clk *ref_clk;
> >         struct mdiobb_ctrl mdiobb;
> >         u32 num_rx_ring[NUM_RX_QUEUE];
> >         u32 num_tx_ring[NUM_TX_QUEUE];
> > diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c
> > index bd30505fbc57..4c3f95923ef2 100644
> > --- a/drivers/net/ethernet/renesas/ravb_main.c
> > +++ b/drivers/net/ethernet/renesas/ravb_main.c
> > @@ -2148,6 +2148,18 @@ static int ravb_probe(struct platform_device *pdev)
> >                 goto out_release;
> >         }
> >
> > +       priv->ref_clk = devm_clk_get(&pdev->dev, "txc_refclk");
>
> Please also update the DT bindings[1], to document the optional
> presence of the clock.

I am not all that familiar with the YAML syntax, but right now, the
clock-names property isn't in the binding, and the driver doesn't use
a name when requesting the single clock it's expecting.
Since the txc_refclk is optional, can the clock-names property allow
for 0-2 names while the number of clocks be 1-2?

clocks:
    minItems: 1
    maxItems: 2

  clock-names:
    minItems: 0
    maxItems: 2
    items:
      enum:
        - fck # AVB functional clock (optional if it is the only clock)
        - txc_refclk # TXC reference clock

With the above proposal, the clock-names would only be necessary when
using the txc_refclk.

>
> > +       if (IS_ERR(priv->ref_clk)) {
> > +               if (PTR_ERR(priv->ref_clk) == -EPROBE_DEFER) {
> > +                       /* for Probe defer return error */
> > +                       error = PTR_ERR(priv->ref_clk);
> > +                       goto out_release;
> > +               }
> > +               /* Ignore other errors since it's optional */
> > +       } else {
> > +               (void)clk_prepare_enable(priv->ref_clk);
>
> This can fail.
> Does this clock need to be enabled all the time?
> At least it should be disabled in the probe failure path, and in
> ravb_remove().

I'll do that for the next rev.

thanks,

adam
>
> [1] Documentation/devicetree/bindings/net/renesas,etheravb.yaml
>
> Gr{oetje,eeting}s,
>
>                         Geert
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-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