linux-kernel - Re: [PATCH] misc/pch_phub: Enable UART clock setting by module parameter

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Date:	Thu, 12 Jul 2012 09:54:06 +0900
From:	Tomoya MORINAGA <tomoya.rohm@...il.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] misc/pch_phub: Enable UART clock setting by module parameter

On Wed, Jul 11, 2012 at 7:45 PM, Arnd Bergmann <arnd@...db.de> wrote:
> This looks like a rather nonscalable solution if you get to systems
> with lots of clocks.

This "clock" is internal clock, not external clock.
This PacketHub provides clock to the UART module
Both the PacketHub and the UART is in 1 chip LSI which is EG20T.
So, selectable clock 1.8432MHz or 48MHz or 64MHz or 192MHz are enough.

> Given that you are doing it for the uart clock, shouldn't that be
> set from the uart driver using an ioctl like other serial ports do?
PacketHub is not serial driver but special driver. So, ioctl doesn't
suit PacketHub.

> What would be the use case for an end user to override the module
> parameter? Is it about platform specific settings or policy?
I show use case.
Currently, UART works with 1.8432MHz.
Using this clock, as you know, maximum speed is 115k.
A user wants to use 4M speed, the user need to modify pch_phun.c by hand.
If this patch is applied, a user can specify uart_clock via a modules
parameter and use 4M speed.

My reference driver for this patch is drivers/tty/serial/pch_uart.c
This driver can set uart_clock via a module parameter(user_uartclk).

Thanks.
-- 
ROHM Co., Ltd.
tomoya
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