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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Date:   Tue, 19 Apr 2022 16:43:13 +0800
From:   Yu Tu <yu.tu@...ogic.com>
To:     Jiri Slaby <jirislaby@...nel.org>,
        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 Jiri,
	Thanks for the tip.

On 2022/4/19 15:38, Jiri Slaby wrote:
> [ EXTERNAL EMAIL ]
> 
> 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.
I got it .This will be corrected in the next version.

> 
>>>> 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,