Re: [PATCH 3/3] arm64: dts: armada-3720-espressobin: wire up LED2

From: "Pali Rohár" <pali@kernel.org>
To: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
Cc: andrew@lunn.ch, gregory.clement@bootlin.com,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 3/3] arm64: dts: armada-3720-espressobin: wire up LED2
Date: Fri, 28 Aug 2020 20:39:01 +0200	[thread overview]
Message-ID: <20200828183901.bkdbcfe3rb25rrk5@pali> (raw)
In-Reply-To: <20180321140616.6maci3xdiwkz2wma@pengutronix.de>

Hello! It is old thread, but I have final results about this issue.

On Wednesday 21 March 2018 15:06:16 Uwe Kleine-König wrote:
> On Wed, Mar 21, 2018 at 02:19:30PM +0100, Andrew Lunn wrote:
> > On Wed, Mar 21, 2018 at 11:50:05AM +0100, Uwe Kleine-K?nig wrote:
> > > The led is connected to MPP1_2.
> > > 
> > > Signed-off-by: Uwe Kleine-K?nig <u.kleine-koenig@pengutronix.de>
> > > ---
> > > Note the LED doesn't work for me on two different boards.
> > 
> > Do you have a board it does work with?
> 
> No, it doesn't work anywhere.
> > 
> > > But the voltage levels on one side of the LED changes from 1.76V to
> > > 0V when enabling the LED. So there is probably something fishy,
> > > don't know if it is hardware or software related.
> > 
> > I think we should not apply this patch until we get a better idea why
> > it does not work.
> 
> Ack. I hoped to get some feedback about this issue.
> 
> > Is 1.76V not enough? Is the LED mounted the wrong way around? Not
> > enough current?
> 
> There is another LED on the board called LED3 that is connected between
> 12V and ground with a R1k that is very bright. It looks identical to the
> non-working LED2 which is connected between 1.8V and MPP1_2 with R100.
> But there is no BOM available that would tell if the led parts are
> different.
> 
> With no PSU connected I can make LED1 and LED3 light up with my
> multimeter, but not LED2.
> 
> I'll try to contact globalscale and ask there.

I contacted globalscale about this issue and I got answer that the led2
on EspressoBin v5 can't be turn on, because of the LED2 vcc use 1.8v,
the voltage is too low to drive the led2.

So it basically answers why that led was not working on any tested
EspressoBin (V5) board.

Also I was told that this hw bug was fixed in EpressoBin v7 revision and
MPP1_2 can be used to control LED2.

So Uwe's patch should be useful for EspressoBin v7 DTS file. On V5 is
LED2 nonworking.

Just to note that LED1 is working fine on EspressoBin V5, it is
controlled by mPCIe card via wlan led pin. So e.g. wifi card which has
supported wlan led driver (e.g. ath9k_pci) can power LED1 on/off.

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