netdev - Re: [PATCH net 3/3] net: dsa: rtl8365mb: set RGMII RX delay in steps of 0.3 ns

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Message-ID: <42ec21b6-07c0-9724-35e2-b4cc2050265f@arinc9.com>
Date:   Mon, 29 Nov 2021 15:27:26 +0300
From:   Arınç ÜNAL <arinc.unal@...nc9.com>
To:     Alvin Šipraga <ALSI@...g-olufsen.dk>,
        Alvin Šipraga <alvin@...s.dk>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>
Subject: Re: [PATCH net 3/3] net: dsa: rtl8365mb: set RGMII RX delay in steps
 of 0.3 ns

Hey Alvin.

On 26/11/2021 16:01, Alvin Šipraga wrote:
> Hi Arınç,
> On 11/26/21 13:57, Arınç ÜNAL wrote:
>>> On 26 Nov 2021, at 15:50, Alvin Šipraga <alvin@...s.dk> wrote:
>>>
>>> From: Alvin Šipraga <alsi@...g-olufsen.dk>
>>>
>>> A contact at Realtek has clarified what exactly the units of RGMII RX
>>> delay are. The answer is that the unit of RX delay is "about 0.3 ns".
>>> Take this into account when parsing rx-internal-delay-ps by
>>> approximating the closest step value. Delays of more than 2.1 ns are
>>> rejected.
>>>
>>> This obviously contradicts the previous assumption in the driver that a
>>> step value of 4 was "about 2 ns", but Realtek also points out that it is
>>> easy to find more than one RX delay step value which makes RGMII work.
>>>
>>> Fixes: 4af2950c50c8 ("net: dsa: realtek-smi: add rtl8365mb subdriver for RTL8365MB-VC")
>>> Cc: Arınç ÜNAL <arinc.unal@...nc9.com>
>>> Signed-off-by: Alvin Šipraga <alsi@...g-olufsen.dk>
>>
>> Acked-by: Arınç ÜNAL <arinc.unal@...nc9.com>
> 
> I know you submitted a device tree using this driver with
> rx-internal-delay-ps = <2000>. Would you care to test your device tree
> with this patch and see if it needs updating? Before this patch, the
> driver would configure a step value of 4. After this patch it will
> configure a step value of 7.
> 
> If you experience problems then we will have to update the device tree
> again, assuming this patch is accepted.
I just tested the driver with this patch on 5.15. The switch seems to 
receive/transmit frames through the cpu port with rx-internal-delay-ps = 
<2000> fine.

Should we update the device tree to use 2100 ps for rx-internal-delay-ps 
anyway?

Arınç