From: Neil Armstrong <narmstrong@baylibre.com>
To: Andy Shevchenko <andy.shevchenko@gmail.com>, Yu Tu <yu.tu@amlogic.com>
Cc: "open list:SERIAL DRIVERS" <linux-serial@vger.kernel.org>,
linux-arm Mailing List <linux-arm-kernel@lists.infradead.org>,
linux-amlogic <linux-amlogic@lists.infradead.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Kevin Hilman <khilman@baylibre.com>,
Jerome Brunet <jbrunet@baylibre.com>,
Jiri Slaby <jirislaby@kernel.org>,
Martin Blumenstingl <martin.blumenstingl@googlemail.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
Date: Thu, 21 Apr 2022 10:46:57 +0200 [thread overview]
Message-ID: <ea86eee0-409c-2d19-3669-35a8eaded53e@baylibre.com> (raw)
In-Reply-To: <CAHp75VeW65dV9jJu8-yUWME+XKnaxZBu5Zv8iEJxP2dizA=HUg@mail.gmail.com>
Hi Andy,
On 18/04/2022 14:09, Andy Shevchenko wrote:
> On Mon, Apr 18, 2022 at 8:50 AM Yu Tu <yu.tu@amlogic.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)
>
>> 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.
>
>> +};
>
> ...
>
>> + unsigned int xtal_div = 3;
>
>> + if (private_data && private_data->has_xtal_div2) {
>> + xtal_div = 2;
>
> Better to define privata data always
While I'm in favor of defining private data, here 3 and 2 are actually the values
2 and 3 used to divide.
The code is easy to read and we quickly understand this value is the clock divider.
>
>
>> + val |= AML_UART_BAUD_XTAL_DIV2;
>> + }
>> + val |= DIV_ROUND_CLOSEST(port->uartclk / xtal_div, baud) - 1;
>
>
next prev parent reply other threads:[~2022-04-21 8:46 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-18 5:32 [PATCH V2 0/2] Add q 12MHz internal clock rate to calculate Yu Tu
2022-04-18 5:32 ` [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 Yu Tu
2022-04-18 12:09 ` Andy Shevchenko
2022-04-19 7:29 ` Yu Tu
2022-04-19 7:38 ` Jiri Slaby
2022-04-19 8:21 ` Andy Shevchenko
2022-04-21 8:44 ` Neil Armstrong
2022-04-19 8:43 ` Yu Tu
2022-04-21 8:46 ` Neil Armstrong [this message]
2022-04-21 9:46 ` Yu Tu
2022-04-18 5:32 ` [PATCH V2 2/2] tty: serial: meson: Added S4 SOC compatibility Yu Tu
2022-04-21 8:49 ` Neil Armstrong
2022-04-21 9:47 ` Yu Tu
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