linux-kernel - Re: [PATCH] net: renesas: Fix rgmii-id delays

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Message-ID: <20211019173520.0154a8cb@kmaincent-XPS-13-7390>
Date:   Tue, 19 Oct 2021 17:35:20 +0200
From:   Köry Maincent <kory.maincent@...tlin.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     netdev <netdev@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Sergey Shtylyov <s.shtylyov@....ru>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>,
        Biju Das <biju.das.jz@...renesas.com>,
        Sergei Shtylyov <sergei.shtylyov@...il.com>,
        Andrew Lunn <andrew@...n.ch>, Adam Ford <aford173@...il.com>,
        Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
        Yang Yingliang <yangyingliang@...wei.com>
Subject: Re: [PATCH] net: renesas: Fix rgmii-id delays

Hello Geert,

Thanks for the review.

On Tue, 19 Oct 2021 17:13:52 +0200
Geert Uytterhoeven <geert@...ux-m68k.org> wrote:

> > The ravb MAC is adding RX delay if RGMII_RXID is selected and TX delay
> > if RGMII_TXID but that behavior is wrong.
> > Indeed according to the ethernet.txt documentation the ravb configuration  
> 
> Do you mean ethernet-controller.yaml?

Doh, yes, I paste the commit log from the older Kernel git and forget to
change that.

> 
> > should be inverted:
> >   * "rgmii-rxid" (RGMII with internal RX delay provided by the PHY, the MAC
> >      should not add an RX delay in this case)
> >   * "rgmii-txid" (RGMII with internal TX delay provided by the PHY, the MAC
> >      should not add an TX delay in this case)
> >
> > This patch inverts the behavior, i.e adds TX delay when RGMII_RXID is
> > selected and RX delay when RGMII_TXID is selected.
> >
> > Signed-off-by: Kory Maincent <kory.maincent@...tlin.com>  
> 
> Does this fix an actual problem for you?

In fact, this fix a problem for an older 4.14 Kernel on my current project.
I wanted to push my fix in the mainline kernel also, but as you say below, now
this code is legacy.
Does it matter to fix legacy code?

> Note that in accordance with the comment above, the code section
> below is only present to support old DTBs.  Contemporary DTBs rely
> on the now mandatory "rx-internal-delay-ps" and "tx-internal-delay-ps"
> properties instead.
> Hence changing this code has no effect on DTS files as supplied with
> the kernel, but may have ill effects on DTB files in the field, which
> rely on the current behavior.

When people update the kernel version don't they update also the devicetree?

Regards,
Köry