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Re: [Xen-devel] Having a DOM-U guest with 1:1 mapping in the second stage MMU.


On 01/04/2020 20:58, Andrei Cherechesu wrote:
I cannot see any issues with the driver. Can you paste the device tree as dom0
sees it? You can access it from /proc/device-tree (you can convert it to dts
with dtc -I fs -O dts). And also the host device tree?

We should see something like the following (this example is taken from a Xilinx

1) host device tree

         serial@ff000000 {
                 compatible = "cdns,uart-r1p12", "xlnx,xuartps";
                 status = "okay";
                 interrupt-parent = <0x4>;
                 interrupts = <0x0 0x15 0x4>;
                 reg = <0x0 0xff000000 0x0 0x1000>;
                 clock-names = "uart_clk", "pclk";
                 power-domains = <0x26 0x21>;
                 clocks = <0x3 0x38 0x3 0x1f>;
                 pinctrl-names = "default";
                 pinctrl-0 = <0x37>;
                 device_type = "serial";
                 port-number = <0x0>;

2) dom0 device tree

     The node is missing

The key is that dom0 should not see the UART node in device tree at all.

If Dom0 is seeing the node, then it is a problem with Xen that somehow is not
hiding it (see "Skip nodes used by Xen" under

If Dom0 is *not* seeing the node, that what is the underlying device tree node
that the dom0 driver is using to bring up /dev/ttyLF0?

I looked under /proc/device-tree and Dom0 actually sees the node corresponding
to the serial device. That means Xen is not hiding it.

I've pasted the host device tree at [0] and the Dom0 device tree at [1]
[0] https://pastebin.com/ir7VkfES
[1] https://pastebin.com/UqRDycHF

So this is the device in the host device tree:

     uart0:serial@401C8000 {
         compatible = "fsl,s32-linflexuart";
         reg = <0x0 0x401C8000 0x0 0x3000>;
         interrupts = <0 82 1>;
         clocks = <&clks S32GEN1_CLK_LIN_BAUD>,
                 <&clks S32GEN1_CLK_LIN>;
         clock-names = "lin", "ipg";
         dmas = <&edma0 0 4>,
                 <&edma0 0 3>;
         dma-names = "rx", "tx";

And this is the device in the Dom0 device tree:

     serial@401C8000 {
         clock-names = "lin\0ipg";
         interrupts = <0x00 0x52 0x01>;
         clocks = <0x04 0x2a 0x04 0x2b>;
         dma-names = "rx\0tx";
         compatible = "fsl,s32-linflexuart";
         reg = <0x00 0x401c8000 0x00 0x3000>;
         dmas = <0x0e 0x00 0x04 0x0e 0x00 0x03>;

 From this story I figured out something else: that I was not passing to Xen's
bootargs "console=dtuart dtuart=serial0". Maybe that's why Xen is not hiding
the node from Dom0 (serial0 is an alias to uart0).

Xen is not going to hide the UART from dom0 if it is not used by the console driver.

So I went on and I added that to bootargs. And now my Xen boot stops here
(DEBUG print on):
(XEN) fixed up name for siul2_reg@0x4401170C -> siul2_reg
(XEN) fixed up name for siul2_reg@0x4401174C -> siul2_reg
(XEN) fixed up name for usbmisc@44064200 -> usbmisc
(XEN) fixed up name for usb@44064000 -> usb
(XEN) fixed up name for memory_DDR0@80000000 -> memory_DDR0
(XEN) fixed up name for memory_DDR1@c0000000 -> memory_DDR1
(XEN) fixed up name for memory_DDR2@880000000 -> memory_DDR2
(XEN)  <- unflatten_device_tree()
(XEN) adding DT alias:can0: stem=can id=0 node=/flexcan@401B4000
(XEN) adding DT alias:can1: stem=can id=1 node=/flexcan@401BE000
(XEN) adding DT alias:can2: stem=can id=2 node=/flexcan@402A8000
(XEN) adding DT alias:can3: stem=can id=3 node=/flexcan@402B2000
(XEN) adding DT alias:serial0: stem=serial id=0 node=/serial@401C8000
(XEN) adding DT alias:serial1: stem=serial id=1 node=/serial@401CC000
(XEN) adding DT alias:serial2: stem=serial id=2 node=/serial@402BC000
(XEN) Platform: Generic System
(XEN) Looking for dtuart at "serial0", options ""
(XEN) DT: ** translation for device /serial@401C8000 **
(XEN) DT: bus is default (na=2, ns=2) on /
(XEN) DT: translating address:<3> 00000000<3> 401c8000<3>
(XEN) DT: reached root node
(XEN) dt_device_get_raw_irq: dev=/serial@401C8000, index=0
(XEN)  intspec=0 intlen=3
(XEN)  intsize=3 intlen=3
(XEN) dt_irq_map_raw: par=/interrupt-controller@50800000,intspec=[0x00000000 
(XEN) dt_irq_map_raw: ipar=/interrupt-controller@50800000, size=3
(XEN)  -> addrsize=2
(XEN)  -> got it�

I started debugging and I found out that it hangs in:
console_init_preirq() -> __putstr(xen_banner()) -> sercon_puts() -> serial_puts() 
-> __serial_putc(),
where it spins at line 178:
         /* Synchronous finite-capacity transmitter. */
         while ( !(n = port->driver->tx_ready(port)) )
Which is a bit strange, considering that my serial device is asynchronous,
I think it should not get there. But it gets on that "else" branch because
port->txbuf is actually NULL at line 120 when it performs the check, and
it does not enter the branch for asynchronous transmitters.

The console is initialized much before the interrupt subsystem is initialized. Therefore you need synchronous support for some part of the boot.

Also, looking at your driver, you don't seem to call serial_async_transmist() in console_init_postirq() (see ns16550.c) so I am not sure how asynchronous would work.


Julien Grall



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