linux-kernel - Re: [PATCH 0/4] pch_uart: Cleanups, board quirks, and user uartclk parameter

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Message-ID: <CANKRQni9E6NO39MFSak6MjQ0DtmQeviGo966Ex9ZUvai56wCjg@mail.gmail.com>
Date:	Wed, 22 Feb 2012 12:10:10 +0900
From:	Tomoya MORINAGA <tomoya.rohm@...il.com>
To:	Darren Hart <dvhart@...ux.intel.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Feng Tang <feng.tang@...el.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Alan Cox <alan@...ux.intel.com>, linux-serial@...r.kernel.org
Subject: Re: [PATCH 0/4] pch_uart: Cleanups, board quirks, and user uartclk parameter

2012年2月22日10:59 Darren Hart <dvhart@...ux.intel.com>:
> This series does some minor clean-up to the pch_uart driver, adds support
> for the Fish River Island II UART clock, and introduces a user_uartclk
> parameter to aid in developing for early and changing hardware.
>
> Note that this series is my proposed alternative solution to that provided
> by Tomoya MORNIAGA and Feng Tang which drops the board quirks and opts to
> assume a 192 MHz clock on all boards. The problem with this approach is
> that the CLKCFG register may have been set to something other than the
> 192MHz configuration by the firmware. If so, then the pch_uart will send
> garbage between the time the boot console is disabled and the pch_phub
> sets the CLKCFG register again. In my case, the pch_phub PCI probe occurs
> after the pch_uart_console_setup. Even if it happened before, the output
> up until the PCI probing would be garbage.
>
> In order to support an early serial console, we cannot rely on the pch_phub
> probe function to setup the CFGCLK register. This series relies on the board
> quirks and doesn't force the setting of the CLKREG in the pch_phub code.
> Instead, it aligns with what is the default configuration (defined by firmware)
> for a given board. The user_uartclk provides a mechanism to force a specific
> uartclk if necessary.

I think UART console function(including "early serial console") is
used for debug use.

So, if people who want to see the boot log correctly before pch_phub installed,
the people have only to do configure uart_clock by themselves.

So, I think default uart_clock 192MHz setting is better than Darren's opinion.

Let me know your opinion.

thanks,

---
ROHM Co., Ltd.
tomoya
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