linux-kernel - Re: [PATCH V6 4/5] tty: serial: meson: Make some bit of the REG5 register writable

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Date:   Thu, 20 Jan 2022 22:49:28 +0100
From:   Jerome Brunet <jbrunet@...libre.com>
To:     Yu Tu <yu.tu@...ogic.com>, linux-serial@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-amlogic@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Neil Armstrong <narmstrong@...libre.com>,
        Kevin Hilman <khilman@...libre.com>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Subject: Re: [PATCH V6 4/5] tty: serial: meson: Make some bit of the REG5
 register writable


On Tue 18 Jan 2022 at 11:09, Yu Tu <yu.tu@...ogic.com> wrote:

> The UART_REG5 register defaults to 0. The console port is set in
> ROMCODE. But other UART ports default to 0, so make bit24 and
> bit[26,27] writable so that the UART can choose a more
> appropriate clock.

Suggestion: Instead of talking bits (which is a bit cryptic) tell us
what is actually does

Something like:
 Make the internal clock source mux and divider writeable, allowing the
 uart to deviate from the settings intially applied by the ROMCode and
 using the most appropriate clocks

>
> Signed-off-by: Yu Tu <yu.tu@...ogic.com>
> ---
>  drivers/tty/serial/meson_uart.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/tty/serial/meson_uart.c b/drivers/tty/serial/meson_uart.c
> index 92fa91c825e6..4e7b2b38ab0a 100644
> --- a/drivers/tty/serial/meson_uart.c
> +++ b/drivers/tty/serial/meson_uart.c
> @@ -678,7 +678,7 @@ static int meson_uart_probe_clocks(struct uart_port *port)
>  							CLK_SET_RATE_NO_REPARENT,
>  							port->membase + AML_UART_REG5,
>  							26, 2,
> -							CLK_DIVIDER_READ_ONLY,
> +							CLK_DIVIDER_ROUND_CLOSEST,
>  							xtal_div_table, NULL);
>  		if (IS_ERR(hw))
>  			return PTR_ERR(hw);
> @@ -708,7 +708,7 @@ static int meson_uart_probe_clocks(struct uart_port *port)
>  					CLK_SET_RATE_PARENT,
>  					port->membase + AML_UART_REG5,
>  					24, 0x1,
> -					CLK_MUX_READ_ONLY,
> +					CLK_MUX_ROUND_CLOSEST,
>  					NULL, NULL);
>  	if (IS_ERR(hw))
>  		return PTR_ERR(hw);