linux-kernel - Re: [PATCH V2 1/2] tty: serial: meson: Add a 12MHz internal clock rate to calculate baud rate in order to meet the baud rate requirements of special BT modules

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Message-ID: <9af92c78-73a7-d524-182c-3ebffa69b08a@kernel.org>
Date:   Tue, 19 Apr 2022 09:38:36 +0200
From:   Jiri Slaby <jirislaby@...nel.org>
To:     Yu Tu <yu.tu@...ogic.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
        linux-amlogic <linux-amlogic@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Neil Armstrong <narmstrong@...libre.com>,
        Kevin Hilman <khilman@...libre.com>,
        Jerome Brunet <jbrunet@...libre.com>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Subject: Re: [PATCH V2 1/2] tty: serial: meson: Add a 12MHz internal clock
 rate to calculate baud rate in order to meet the baud rate requirements of
 special BT modules

Hi,

On 19. 04. 22, 9:29, Yu Tu wrote:
> Hi Andy,
>      Thank you for your advice.
> 
> On 2022/4/18 20:09, Andy Shevchenko wrote:
>> [ EXTERNAL EMAIL ]
>>
>> On Mon, Apr 18, 2022 at 8:50 AM Yu Tu <yu.tu@...ogic.com> wrote:
>>>
>>> A /2 divider over XTAL was introduced since G12A, and is preferred
>>> to be used over the still present /3 divider since it provides much
>>> closer frequencies vs the request baudrate.Especially the BT module
>>
>> 'e. E' (mind the space)
> My statement is a whole. There should be no spaces.

Period should be followed by a space, of course.

>>> uses 3Mhz baud rate. 8Mhz calculations can lead to baud rate bias,
>>> causing some problems.
>>
>> ...
>>
>>> +struct meson_uart_data {
>>> +       bool has_xtal_div2;
>>
>> I would prefer to see this as an unsigned int and with a less
>> particular name, e.g. xtal_div would suffice.
> I don't have a problem with your suggestion.Let's see What Neil has to say.

Actually why uint provided it's a boolean value? Or do you mean to store 
the divisor directly in this member, Andy?

thanks,
-- 
js
suse labs