linux-kernel - Re: [RFC. PATCH] earlycon: Remove hardcoded port->uartclk initialization in of_setup

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Date:   Mon, 23 Apr 2018 15:22:51 +0200
From:   Michal Simek <michal.simek@...inx.com>
To:     Matt Redfearn <matt.redfearn@...s.com>,
        Michal Simek <michal.simek@...inx.com>,
        <linux-kernel@...r.kernel.org>, <monstr@...str.eu>,
        <devicetree@...r.kernel.org>, Rob Herring <robherring2@...il.com>
CC:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        <linux-serial@...r.kernel.org>, Jiri Slaby <jslaby@...e.com>
Subject: Re: [RFC. PATCH] earlycon: Remove hardcoded port->uartclk
 initialization in of_setup_earlycon

Hi,

On 23.4.2018 15:16, Matt Redfearn wrote:
> 
> 
> On 23/04/18 10:27, Michal Simek wrote:
>> There is no reason to initialize uartclk to BASE_BAUD * 16 for DT based
>> systems.
>>
>> Signed-off-by: Michal Simek <michal.simek@...inx.com>
>> ---
>>
>> It looks like from history that portclk = BASE_BAUD * 16 was setup to
>> get on calculation on x86 (divisor = 1) but it shouldn't be needed on
>> DT based
>> system. That's why I think that there is no DT based system which really
>> requires this line.
> 
> Hi Michal,
> 
> This is fine for the MIPS generic platform (tested on Boston board)
> which was broken by some earlycon changes a few versions ago. Also
> tested on a MIPS pistachio board. As long as the bootloader has
> configured the uart divisor, earlycon should work as long as my patch
> "serial: 8250_early: Only set divisor if valid clk & baud" is applied to
> avoid a bad divisor getting calculated.

I have sent one patch to fix your patch because you don't need to check
device->baud twice.
[PATCH] serial: 8250_early: Setup divider when uartclk is passed
 > Tested-by: Matt Redfearn <matt.redfearn@...s.com>

Thanks,
Michal