[yocto] thud, beaglebone-yocto.conf: SERIAL_CONSOLES setting

Sat Nov 3 01:37:13 PDT 2018

On Fri, Nov 02, 2018 at 07:27:04AM -0700, Khem Raj wrote:
> On Fri, Nov 2, 2018 at 2:02 AM Kevin Hao <kexin.hao at windriver.com> wrote:
> >
> > On Fri, Nov 02, 2018 at 09:01:34AM +0100, Heiko Schocher wrote:
> > > Hello Kevin,
> > >
> > > Am 01.11.2018 um 03:18 schrieb Kevin Hao:
> > > > On Wed, Oct 31, 2018 at 02:23:00PM +0100, Heiko Schocher wrote:
> > > > > Hello all,
> > > > >
> > > > > just builded core-image-minimal with current head of thud branch for
> > > > > the beaglebone-yocto machine, with linux 4.14.x LTS "Linux version 4.14.78",
> > > > > installed the resulting sd card image and boot it, and get:
> > > > >
> > > > > INIT: Id "O0" respawning too fast: disabled for
> > > > > 5 minutes
> > > > >
> > > > > Reason seems to be:
> > > > >
> > > > > meta-yocto-bsp/conf/machine/beaglebone-yocto.conf
> > > > >
> > > > > SERIAL_CONSOLES = "115200;ttyO0"
> > > > >
> > > > > shouldn't this be
> > > > >
> > > > > SERIAL_CONSOLES = "115200;ttyS0"
> > > > >
> > > > > With this fix, sd card image boot fine ... may I oversee seomthing
> > > > > obvious ?
> > > >
> > > > No, it should be 'ttyO0'. It is set by the omap serial driver. You can
> > > > refer the following in platform_data/serial-omap.h:
> > > >    #define OMAP_SERIAL_NAME        "ttyO"
> > >
> > > Yes, you are right, but I see with linux kernel 4.14.78 from
> > >
> > > https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=linux-4.14.y&id=e7405910ca5553eae8744af4e5c03e64ee048cb1
> > >
> > > and I see:
> > >
> > > [    0.000000] Linux version 4.14.78 (oe-user at oe-host) (gcc version 8.2.0
> > > (GCC)) #1 Thu Nov 1 10:51:09 UTC 2018
> > > [    0.000000] CPU: ARMv7 Processor [413fc082] revision 2 (ARMv7), cr=10c5387d
> > > [    0.000000] CPU: PIPT / VIPT nonaliasing data cache, VIPT aliasing instruction cache
> > > [    0.000000] OF: fdt: Machine model: TI AM335x BeagleBone Black
> > > [...]
> > > [    0.362878] Serial: 8250/16550 driver, 6 ports, IRQ sharing disabled
> > > [    0.365758] 44e09000.serial: ttyS0 at MMIO 0x44e09000 (irq = 30, base_baud = 3000000) is a 8250
> > > [    1.030465] console [ttyS0] enabled
> > >
> > > So definitely a ttyS0 ...
> >
> > OK, so you don't use the linux-yocto kernel, you must not use the Yocto kernel
> > meta either.
> 
> I dont think there is such a rule.

I don't get what you mean about such a rule. I didn't say anything about that.
I just pointed out why Heiko get stuck by that issue and how to workaround it.

> meta-yocto-bsps are meant as
> references and people might want to enhance them.

Of course, that is also why we are continually working on it.

> 
>  The reason that you got a ttyS0 here is that you use the
> > 8250_omap.c driver. But in Yocto we use the omap-serial.c driver. You can
> > workaround this issue by enabling SERIAL_8250_OMAP_TTYO_FIXUP.
> >
> 
> omap serial is obsolete why does linux-yocto keeps using it.

I guess that the original reason that we use this should be something like the
comments in the omap-serial.c:
 * Note: This driver is made separate from 8250 driver as we cannot
 * over load 8250 driver with omap platform specific configuration for
 * features like DMA, it makes easier to implement features like DMA and
 * hardware flow control and software flow control configuration with
 * this driver as required for the omap-platform.

Yes, it has been a long time since the comments were written and even before the
birth of the 8250_omap.c. But I am just not sure that the 8250_omap driver
is mature enough so we can switch to it safely and we also don't get any serial
issue so far. That is why we leave it as is. And it also seem that the omap-serial.c
is also enabled by default in both the multi_v7_defconfig and omap2plus_defconfig
in the latest kernel:
  $ git grep "CONFIG_SERIAL_OMAP" arch/arm/
  arch/arm/configs/multi_v7_defconfig:CONFIG_SERIAL_OMAP=y
  arch/arm/configs/multi_v7_defconfig:CONFIG_SERIAL_OMAP_CONSOLE=y
  arch/arm/configs/omap2plus_defconfig:CONFIG_SERIAL_OMAP=y
  arch/arm/configs/omap2plus_defconfig:CONFIG_SERIAL_OMAP_CONSOLE=y

But if you are pretty sure that the 8250_omap.c is mature enough and also
provide more functions than omap-serial.c, please send a patch and we can
definitely switch the serial driver to that.

> seondly, machine config should enable both consoles ttyO0 and ttyS0 if
> you know that at least one kernel is using ttyO0

Yes, this is an option to fix this issue. Do you mind send a patch?

Thanks,
Kevin

> 
> > Thanks,
> > Kevin
> >
> > >
> > > bye,
> > > Heiko
> > > >
> > > > Thanks,
> > > > Kevin
> > > >
> > > > >
> > > > > bye,
> > > > > Heiko
> > > > > --
> > > > > DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
> > > > > HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
> > > > > Phone: +49-8142-66989-52   Fax: +49-8142-66989-80   Email: hs at denx.de
> > > > > --
> > > > > _______________________________________________
> > > > > yocto mailing list
> > > > > yocto at yoctoproject.org
> > > > > https://lists.yoctoproject.org/listinfo/yocto
> > >
> > > --
> > > DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
> > > HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
> > > Phone: +49-8142-66989-52   Fax: +49-8142-66989-80   Email: hs at denx.de
> > --
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