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: <8a6fd8c4-d6ea-973e-4344-773b70c46b15@bang-olufsen.dk>
Date:   Mon, 29 Nov 2021 12:46:23 +0000
From:   Alvin Šipraga <ALSI@...g-olufsen.dk>
To:     Arınç ÜNAL <arinc.unal@...nc9.com>,
        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

Hi Arınç,

On 11/29/21 13:27, Arınç ÜNAL wrote:
> 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.

Great, thanks a lot for testing!

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

Under the hood the driver will do the same thing, so it's not necessary.

> 
> Arınç