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

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Date:   Fri, 26 Nov 2021 13:01:57 +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 11/26/21 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.

Thanks!

	Alvin