Hi Paul,

From: Paul Fertser <fercerpav@gmail.com>
Sent: Wednesday, September 8, 2021 5:43 PM

Hello,

On Thu, Sep 02, 2021 at 10:18:13AM +0800, Chia-Wei Wang wrote:

quoted

Add UART routing driver and the device tree nodes.

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 similar
approaches!


One (somewhat) related question that I hope you do not mind answering:
is there anything special regarding the routing or other configuration that
needs to be done for VUART to work with IRQs?

No. The routing control has no relation to VUART.

The reason I ask is that I have tried hard (and I know several other developers
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 is 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 toggling it
manually the data was getting through.

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.

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

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