linux-kernel - Re: [PATCH] pch_uart: Change default UART clock setting 192MHz

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Date:	Tue, 21 Feb 2012 16:20:52 -0800
From:	Darren Hart <dvhart@...ux.intel.com>
To:	Tomoya MORINAGA <tomoya.rohm@...il.com>
CC:	Alan Cox <alan@...ux.intel.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
	qi.wang@...el.com, yong.y.wang@...el.com, joel.clark@...el.com,
	kok.howg.ewe@...el.com, feng.tang@...el.com
Subject: Re: [PATCH] pch_uart: Change default UART clock setting 192MHz

On 02/21/2012 03:43 PM, Tomoya MORINAGA wrote:
> 2012年2月22日1:07 Darren Hart <dvhart@...ux.intel.com>:
>>  When does the phub driver update the clock registers?
> 
> I've already posted pch_phub patch for 192MHz setting.
> You can see the patch form below.

Yes, I applied the patch. The problem seems to be this:

DVHART: parse_options (8250_early.c)
DVHART: pch_console_setup                                                           
DVHART: pch_console_setup                                                           
DVHART: pch_phub_probe: set CLKCFG UART to 192MHz      

As you can see, the pch_phub_probe happens much too late.

I can get it to work with a boot command line like this:
earlycon=uart8250,io,0x2050,115200n8 console=ttyPCH1,115200n8

And hacking all the BASE_BAUD references to be 48000000
(my current hardware sets the clock to 48MHz in firmware).
This gets things working until pch_phub gets around to setting
the CLKCFG register for the UART clock.

I'd prefer to not have to use the earlycon parameter/code,
but we need a way for the pch_uart to understand the difference
between early boot and post-phub setup. Can we read the CLKCFG
register in pch_console_setup to dynamically configure the
port->uartclk? (not sure that's even the right place to do it).

--
Darren

>>> Signed-off-by: Tomoya MORINAGA <tomoya.rohm@...il.com>
>>> ---
>>> Related patch is
>>> http://marc.info/?l=linux-kernel&m=132979974907774&w=2
> 
> ---
> ROHM Co., Ltd.
> tomoya

-- 
Darren Hart
Intel Open Source Technology Center
Yocto Project - Linux Kernel
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