Re: [PATCH] net: dsa: mt7530: disable LEDs before reset

From: Daniel Golle <daniel@makrotopia.org>
To: "Arınç ÜNAL" <arinc.unal@arinc9.com>
Cc: patchwork-bot+netdevbpf@kernel.org,
	Justin Swartz <justin.swartz@risingedge.co.za>,
	dqfext@gmail.com, sean.wang@mediatek.com, andrew@lunn.ch,
	f.fainelli@gmail.com, olteanv@gmail.com, davem@davemloft.net,
	edumazet@google.com, kuba@kernel.org, pabeni@redhat.com,
	matthias.bgg@gmail.com, 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: disable LEDs before reset
Date: Mon, 11 Mar 2024 21:58:50 +0000	[thread overview]
Message-ID: <Ze9-mp269h43WGD3@makrotopia.org> (raw)
In-Reply-To: <2d206dbb-a27b-4139-a49e-331797d8ba34@arinc9.com>

On Tue, Mar 12, 2024 at 12:22:48AM +0300, Arınç ÜNAL wrote:
> Why was this applied? I already explained it did not achieve anything.

I agree that we were still debating about it, however, I do believe
Justin that he truely observed this problem and the fix seemed
appropriate to me.

I've explained this in my previous email which you did not notice
or at least haven't repied to:

https://patchwork.kernel.org/project/netdevbpf/patch/20240305043952.21590-1-justin.swartz@risingedge.co.za/#25753421

In the end it probably depends on the electric capacity of the circuit
connecting each LED, so it may not be reproducible on all boards and/or
under all circumstances (temperature, humindity, ...).

Disabling the LEDs and waiting for around 1mS before reset seems like
a sensible thing to do, and I'm glad Justin took care of it.

> 
> Arınç
> 
> On 12.03.2024 00:10, patchwork-bot+netdevbpf@kernel.org wrote:
> > Hello:
> > 
> > This patch was applied to netdev/net-next.git (main)
> > by Jakub Kicinski <kuba@kernel.org>:
> > 
> > On Tue,  5 Mar 2024 06:39:51 +0200 you wrote:
> > > Disable LEDs just before resetting the MT7530 to avoid
> > > situations where the ESW_P4_LED_0 and ESW_P3_LED_0 pin
> > > states may cause an unintended external crystal frequency
> > > to be selected.
> > > 
> > > The HT_XTAL_FSEL (External Crystal Frequency Selection)
> > > field of HWTRAP (the Hardware Trap register) stores a
> > > 2-bit value that represents the state of the ESW_P4_LED_0
> > > and ESW_P4_LED_0 pins (seemingly) sampled just after the
> > > MT7530 has been reset, as:
> > > 
> > > [...]
> > 
> > Here is the summary with links:
> >    - net: dsa: mt7530: disable LEDs before reset
> >      https://git.kernel.org/netdev/net-next/c/2920dd92b980
> > 
> > You are awesome, thank you!