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

From: "Arınç ÜNAL" <arinc.unal@arinc9.com>
To: Justin Swartz <justin.swartz@risingedge.co.za>
Cc: Daniel Golle <daniel@makrotopia.org>,
	DENG Qingfang <dqfext@gmail.com>,
	Sean Wang <sean.wang@mediatek.com>, Andrew Lunn <andrew@lunn.ch>,
	Florian Fainelli <f.fainelli@gmail.com>,
	Vladimir Oltean <olteanv@gmail.com>,
	"David S. Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	Matthias Brugger <matthias.bgg@gmail.com>,
	AngeloGioacchino Del Regno
	<angelogioacchino.delregno@collabora.com>,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-mediatek@lists.infradead.org
Subject: Re: [PATCH] net: dsa: mt7530: increase reset hold time
Date: Wed, 13 Mar 2024 18:04:43 +0300	[thread overview]
Message-ID: <997db446-030b-4e6a-beea-0ae7d990e7e2@arinc9.com> (raw)
In-Reply-To: <c4590e9519d0cd788d157a1e1510cc45@risingedge.co.za>

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

> 
> 
>> 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.

Arınç