[U-Boot] [U-Boot-DM] [PATCH] drivers: serial: probe all serial devices

[Wolfgang Denk]

Dear Vabhav,

In message <VI1PR04MB48005B3CB205F14C4670CC2BF3F70 at VI1PR04MB4800.eurprd04.prod.outlook.com> you wrote:
> 
> > U-Boot does lazy initialization intentionally.  It is wrong to initialize devices
> > which are not actually used.

> There is configuration option to enable the device using platform
> data or device tree using DM model.

"enable" means we have all required information needed to initialize
them, if we need them.  The need arises only when someone wants to
transfer data over that UART.  If nobody uses the UArt, there is no
need to ever initialize it.

Lazy initialization is a good thing - it saves resources, especially
memory and time.  Think for example of boot time optimizations...

> For e.g: 2 UART controllers are enabled in device tree but DM
> model initialized only one, This is limitation

In which way is this a limitation?  We use only one UART (for the
serial console), so it works as supposed: only the used devices are
fully initialized.


> My suggestion is to initialize all devices which are enabled, E.g.
> use case is using UART1 for uboot consoled and UART2 for linux boot

What do you mean "for Linux boot"?  If Linux needs the UART, it will
initialize it itself in the Linux dvice driver.

> On NXP SoC, We also use UART3 for ethernet firmware logging but
> using DM model all enabled devices are not probed  posing
> limitation.

Again, this is intentional, and not a limitation.

And what exactly do you mean by "UART3 for ethernet firmware
logging"?

Maybe you should rethink your software concept.  We don't want to
have a zillion of ports in used if not really necessary.  Either you
use standard channels (STDOUT, STDERR) for logging.  Also, there
used to be a syslog compatible logging driver.

> > I have a feeling that you attempt to do the Wong Thing.

> I quoted the reason above and also discussed on in email(23 may) "
> [U-Boot-DM] QUERY:U-boot DM:SERIAL:Multiple On-chip UART
> Controller Support" with suggested solution from Simon which is
> sent as patch for review.

But Simon also explained "U-Boot only probes things in a 'lazy'
manner so far", and there should be really good reasons for
deviating from this principle.  In no way should a "probe all
devices" be made the default.

And Andreas also wrote how to solve this issue in a board-specific
way if it is really, really needed on some board.

However, you still fail to explain why you ned multiple serial ports
in U-Boot running in parallel.

Best regards,

Wolfgang Denk

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