netdev - Re: [PATCH] net: dsa: mt7530: increase reset hold time

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Message-ID: <3146df060620f08a620417cfcf2b2179@risingedge.co.za>
Date: Wed, 13 Mar 2024 17:38:35 +0200
From: Justin Swartz <justin.swartz@...ingedge.co.za>
To: Arınç ÜNAL <arinc.unal@...nc9.com>
Cc: Daniel Golle <daniel@...rotopia.org>, DENG Qingfang <dqfext@...il.com>,
 Sean Wang <sean.wang@...iatek.com>, Andrew Lunn <andrew@...n.ch>, Florian
 Fainelli <f.fainelli@...il.com>, Vladimir Oltean <olteanv@...il.com>, "David
 S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub
 Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Matthias
 Brugger <matthias.bgg@...il.com>, AngeloGioacchino Del Regno
 <angelogioacchino.delregno@...labora.com>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH] net: dsa: mt7530: increase reset hold time

On 2024-03-13 17:04, Arınç ÜNAL wrote:
> On 13.03.2024 16:13, Justin Swartz wrote:
>> On 2024-03-13 14:06, Arınç ÜNAL wrote:
>>> On 13.03.2024 14:52, Justin Swartz wrote:
>>>> 
>>>> On 2024-03-13 10:59, Arınç ÜNAL wrote:
>>>>> This ship has sailed anyway. Now the changes the first patch did 
>>>>> must be
>>>>> reverted too. I will deal with this from now on, you can stop 
>>>>> sending
>>>>> patches regarding this.
>>>> 
>>>> At least if the first patch isn't reverted, the approach used is
>>>> less likely to result in the problem occuring, IMHO.
>>> 
>>> I disagree that the previous approach is less likely to result in the
>>> problem occurring. If you don't like the delay amount we agreed on, 
>>> feel
>>> free to express a higher amount.
>> 
>> I created and tested a patch to entertain your input about what you
>> thought could be a suitable hold period to address the problem, and it
>> appeared to work. The criteria being that the crystal frequency 
>> selection
>> was correct over 20 tests.
>> 
>> So if only the reset hold period is going to change, I'm good with 
>> what
>> you had suggested: 5000 - 5100 usec.
>> 
>> Ultimately the selection of this period should be guided by the timing
>> information provided in a datasheet or design guide from the 
>> manufacturer.
> 
> That's a good point, I agree.
> 
>> 
>> If you, or anyone else, has such a document that provides this 
>> information
>> and is able to confirm or deny speculation about any/all timing 
>> periods
>> related to reset, please do so.
> 
> These are the documents I use to program this switch family. I did not
> stumble upon a page going over this.
> 
> MT7621 Giga Switch Programming Guide v0.3:
> 
> https://github.com/vschagen/documents/blob/main/MT7621_ProgrammingGuide_GSW_v0_3.pdf
> 
> MT7531 switch chip datasheet:
> 
> https://wiki.banana-pi.org/Banana_Pi_BPI-R64#Documents

Thanks for the links.

Have you encountered this one?

MT7530 Giga Switch Programming Guide v0.1:
https://github.com/libc0607/arduino_mt7530/blob/master/MT7530_programming_guide_V00.pdf

It has some timing diagrams, but nothing I found for reset.

The HWTRAP description has some bits swapped, so I guess those were 
typos,
in the case of XTAL_SELECT.


>>> I also disagree on introducing a solution that is in addition to 
>>> another
>>> solution, both of which fix the same problem.
>> 
>> I'm not sure I understand why you say that. These patches were 
>> intended
>> to be applied exclusively, or in other words: in isolation - not 
>> together.
>> 
>> Although if they were applied together, it wouldn't really matter.
>> 
>> For the record, I've only continued to keep this thread alive in the
>> hope that some solution to this problem will make it into mainline
>> eventually.
>> 
>> I don't care if it was my original patch, the subsequent patch, or a
>> later patch provided by you or someone else. :)
> 
> I think you've missed that your patch is already applied. And it won't 
> be
> reverted for reasons explained by Paolo in this mail thread.
> 
> https://git.kernel.org/netdev/net-next/c/2920dd92b980
> 
> So if your patch here were to be applied too, the final mt7530.c would 
> have
> the LEDs disabled AND before reset deassertion delay increased.

Yes, I seem to have missed that. I thought your request for the
patch to be reverted definitely would have been performed, or at
least queued, seeing as you're the maintainer.