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From:   ChiaWei Wang <chiawei_wang@aspeedtech.com>
To:     Paul Fertser <fercerpav@gmail.com>
CC:     "robh+dt@kernel.org" <robh+dt@kernel.org>,
        "joel@jms.id.au" <joel@jms.id.au>,
        "andrew@aj.id.au" <andrew@aj.id.au>,
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        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
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        <linux-arm-kernel@lists.infradead.org>,
        "linux-aspeed@lists.ozlabs.org" <linux-aspeed@lists.ozlabs.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "openbmc@lists.ozlabs.org" <openbmc@lists.ozlabs.org>,
        Konstantin Klubnichkin <kitsok@yandex-team.ru>
Subject: RE: [PATCH v2 0/3] arm: aspeed: Add UART routing support
Thread-Topic: [PATCH v2 0/3] arm: aspeed: Add UART routing support
Thread-Index: AQHXn6Ep4pfNy4cUzEmFUBdsNZd0kquZ7IKAgAAENXA=
Date:   Wed, 8 Sep 2021 10:18:35 +0000
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References: <20210902021817.17506-1-chiawei_wang@aspeedtech.com>
 <20210908094248.GZ23326@home.paul.comp>
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Hi Paul,

> From: Paul Fertser <fercerpav@gmail.com>
> Sent: Wednesday, September 8, 2021 5:43 PM
>=20
> Hello,
>=20
> On Thu, Sep 02, 2021 at 10:18:13AM +0800, Chia-Wei Wang wrote:
> > Add UART routing driver and the device tree nodes.
>=20
> Thank you for working on exposing this functionality in upstreamable way,
> that's so much better than all the register-level hacks in U-Boot and sim=
ilar
> approaches!
>=20
>=20
> One (somewhat) related question that I hope you do not mind answering:
> is there anything special regarding the routing or other configuration th=
at
> needs to be done for VUART to work with IRQs?

No. The routing control has no relation to VUART.

>=20
> The reason I ask is that I have tried hard (and I know several other deve=
lopers
> who have too) to use VUART functionality but somehow as soon as Linux was
> booting on host and starting to use the IRQ-based
> 16550 driver the communication was halted both ways. Basically, the BMC
> firmware was enabling VUART in DTS, then setting LPC address to
> 0x3F8 and LPC IRQ to 4 and reading/writing using the corresponding
> /dev/ttyS* node. The datasheet is not clearly telling what other actions =
need to
> be performed for this to work. Not using VUART and instead routing UART1
> lines with exactly the same pinctrl/pinmux worked just fine. One detail i=
s that
> with VUART the host wasn't seeing new interrupts but when they were
> simulated by exporting the LPC interrupt pin via /sys/class/gpio and togg=
ling it
> manually the data was getting through.
>=20
> Does UART1 need some explicit disabling for VUART IRQs to work? It looks =
like
> setting LPC address and IRQ number in VUART is enough to override the
> register part but probably not for the interrupt?

You may need to confirm that the Host does not enable the SIO SUART1 device=
.
This will conflict with VUART as both SUART and VAURT are competing for the=
 port address 0x3f8 and SIRQ 4.

>=20
> --
> Be free, use free (http://www.gnu.org/philosophy/free-sw.html) software!
> mailto:fercerpav@gmail.com