linux-kernel - Re: [PATCH RFC v2 08/11] net: stmmac: dwmac-meson8b: add support for the RX delay configuration

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Message-ID: <CAFBinCCbtLRomdikKWkS+HOFoek4cGhN4L91FQfQ4rbKTV-xvg@mail.gmail.com>
Date:   Fri, 1 May 2020 19:10:06 +0200
From:   Martin Blumenstingl <martin.blumenstingl@...glemail.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     robh+dt@...nel.org, f.fainelli@...il.com,
        linux-amlogic@...ts.infradead.org, devicetree@...r.kernel.org,
        jianxin.pan@...ogic.com, davem@...emloft.net,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH RFC v2 08/11] net: stmmac: dwmac-meson8b: add support for
 the RX delay configuration

Hi Andrew,

On Fri, May 1, 2020 at 5:44 PM Andrew Lunn <andrew@...n.ch> wrote:
>
> > +     if (rx_dly_config & PRG_ETH0_ADJ_ENABLE) {
> > +             /* The timing adjustment logic is driven by a separate clock */
> > +             ret = meson8b_devm_clk_prepare_enable(dwmac,
> > +                                                   dwmac->timing_adj_clk);
> > +             if (ret) {
> > +                     dev_err(dwmac->dev,
> > +                             "Failed to enable the timing-adjustment clock\n");
> > +                     return ret;
> > +             }
> > +     }
>
> Hi Martin
>
> It is a while since i used the clk API. I thought the get_optional()
> call returned a NULL pointer if the clock does not exist.
> clk_prepare_enable() passed a NULL pointer is a NOP, but it also does
> not return an error. So if the clock does not exist, you won't get
> this error, the code keeps going, configures the hardware, but it does
> not work.
>
> I think you need to check dwmac->timing_adj_clk != NULL here, and
> error out if DT has properties which require it.
Thank you for your excellent code review quality (as always)!
you are right and I will fix that in the next version


Martin