Hi Nikita,

On Tue, May 23, 2017 at 08:24:18AM +0300, Nikita Yushchenko wrote:

Hi,

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Alternative solution could be - have separate write path for earlycon.

It looks to me having the same issue with a separate write patch
for earlycon as we still need distinguish Little or Big endian
for Layerscape and IMX.

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At a glance, it is dozen lines of code.

Would you please show some sample code?

Do not reuse lpuart32_console_putchar() in earlycon code.

Have two sets of early_setup/early_write/putchar - for BE and
defaut-endian earlycon. And in these putchar's do not use
lpuart_(read|write).

Isn't that introducing another consistency break after fix one
consistency break?

If doing that, we then have two register read/write APIs.
One for normal driver operation by dynamically checking lpuart_is_be
property to distinguish the endian difference problem.
Another is specifically implemented for only early console read/write
and use hardcoded way to read/write register directly instead of using
the standard API lpuart32_read/write, like follows:
e.g.
lpuart32_le_console_write() {
	 writel();
}

lpuart32_be_console_write() {
	 iowrite32be()
}
This also makes the driver a bit strange and ugly.

It looks to me both way are trade offs and the later one seems sacrifice
more. And i doubt if it's really necessary for probably a no real gain
purpose as the FPGA you mentioned is a theoretical case and less
possibility to exist.

I'm still wondering how about keep using the exist way and adding more
information in code to explain why use a global var?

I've checked other driver under drivers/tty/serial/, for examples of
similar cases.

Please look at serial8250_early_in() / serial8250_early_out() ?
These do handle different endian, via port->iotype

Well, that does inspire me.

With struct uart_port's iotype member, the global lpuart_is_be can be
gone. We can update lpuart32_read/write API to take the reference of
of structure uart_port, then the API knows the endian information and
can use the correct further IO accessor accordingly.

And most importantly, it also works with earlycon.

Another example is drivers/tty/serial/samsung.c, where
port->private_data is initialized and used.

If using iotype, seems no need private_data anymore.
Will try and send the new series later with you CCed to help review.

Thanks for the advice.

Regards
Dong Aisheng