linux-kernel - Re: [PATCH v2 2/2] serial: earlycon: allow to specify uartclk in earlycon kernel-parameter

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <CAK7LNARFOzkBVabThTOyZc28F2Kyt3fXnbJTWO632D1yUdg4oQ@mail.gmail.com>
Date:	Fri, 23 Oct 2015 20:15:33 +0900
From:	Masahiro Yamada <yamada.masahiro@...ionext.com>
To:	Rob Herring <robh@...nel.org>
Cc:	Peter Hurley <peter@...leysoftware.com>,
	Stefan Agner <stefan@...er.ch>,
	"linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jiri Slaby <jslaby@...e.com>
Subject: Re: [PATCH v2 2/2] serial: earlycon: allow to specify uartclk in
 earlycon kernel-parameter

2015-10-23 0:34 GMT+09:00 Rob Herring <robh@...nel.org>:
> On Tue, Oct 20, 2015 at 8:20 PM, Masahiro Yamada
> <yamada.masahiro@...ionext.com> wrote:
>> Hi Peter,
>> (+ Rob Herring, Stefan Agner)
>>
>> 2015-10-20 23:00 GMT+09:00 Peter Hurley <peter@...leysoftware.com>:
>>> On 10/19/2015 11:36 PM, Masahiro Yamada wrote:
>>>> The input clock frequency varies from device to device, but the
>>>> earlycon uses the fixed frequency (BASE_BAUD * 16).  It makes
>>>> impossible to set the correct divisor to the register.
>>>
>>> So the bootloader hasn't setup the serial port?
>>
>> It does.
>> I use U-boot and the serial port is already set up by U-boot.
>
> This problem is now moving into u-boot which is using DT for configuration.
>
>> But, earlycon setup functions update hardware registers.
>> See  early_serial8250_setup(), ingenic_early_console_setup(), etc.
>>
>>
>> Without port->uartclk set to a valid value,
>> the init code in earlycon setup does not make sense.
>>
>>
>> What I want to clarify is,
>> what should we do in the earlycon setup function?
>>
>> Currently, I see
>>  [1] set device->con->write callback
>>  [2] initialize UART port registers
>>
>>
>> For [2], we need to know baudrate and input clock frequency.
>> (and the latter is missing, that's why my patch is here.)
>
> I'm missing context of what you did, but it needs to be parse-able
> from a flattened tree. My suggestion would be use clock-frequency
> property in the uart node. We should be able to parse that. This came
> up with u-boot as well[1].

Right.

But, I think things have been going wrong
since SPL started to parse a device tree.




-- 
Best Regards
Masahiro Yamada
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/