linux-kernel - Re: [PATCH] tty: serial: msm: Remove duplicate handling of clocks

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Date:	Mon, 16 May 2016 14:01:15 +0530
From:	Pramod Gurav <pramod.gurav@...aro.org>
To:	Stephen Boyd <sboyd@...eaurora.org>,
	Andy Gross <andy.gross@...aro.org>, gregkh@...uxfoundation.org,
	David Brown <davidb@...eaurora.org>, jslaby@...e.com
Cc:	linux-arm-msm@...r.kernel.org, linux-serial@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Pramod Gurav <pramod.gurav@...aro.org>
Subject: Re: [PATCH] tty: serial: msm: Remove duplicate handling of clocks

On 11 May 2016 at 14:30, Pramod Gurav <pramod.gurav@...aro.org> wrote:
> msm_serial driver provides a .pm callback to the serial core to enable
> and disable clock resource in suspend/resume path. This function is
> also called before msm_startup. msm_startup also enables the clocks which
> is not needed. Hence remove the duplcate clock operation from msm_startup
> and msm_shutdown. Same is done in console setup to get rid of duplicate
> clock operation.
>
> Tested on DB410C console.
>
> Signed-off-by: Pramod Gurav <pramod.gurav@...aro.org>
> ---
>  drivers/tty/serial/msm_serial.c | 15 ++-------------
>  1 file changed, 2 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/tty/serial/msm_serial.c b/drivers/tty/serial/msm_serial.c
> index dcde955..73c3217 100644
> --- a/drivers/tty/serial/msm_serial.c
> +++ b/drivers/tty/serial/msm_serial.c
> @@ -959,15 +959,6 @@ static int msm_set_baud_rate(struct uart_port *port, unsigned int baud,
>         return baud;
>  }
>
> -static void msm_init_clock(struct uart_port *port)
> -{
> -       struct msm_port *msm_port = UART_TO_MSM(port);
> -
> -       clk_prepare_enable(msm_port->clk);
> -       clk_prepare_enable(msm_port->pclk);
> -       msm_serial_set_mnd_regs(port);
> -}
> -
>  static int msm_startup(struct uart_port *port)
>  {
>         struct msm_port *msm_port = UART_TO_MSM(port);
> @@ -982,7 +973,7 @@ static int msm_startup(struct uart_port *port)
>         if (unlikely(ret))
>                 return ret;
>
> -       msm_init_clock(port);
> +       msm_serial_set_mnd_regs(port);

Further testing with another UART port made me realize that serial
port does not work after disabling msm_port->clk clock. The RX data
part will be affected.
Confirmed from manual that this clock should never be turned of to
avoid loss of incoming data. Sorry for the noise.

>
>         if (likely(port->fifosize > 12))
>                 rfr_level = port->fifosize - 12;
> @@ -1021,8 +1012,6 @@ static void msm_shutdown(struct uart_port *port)
>         if (msm_port->is_uartdm)
>                 msm_release_dma(msm_port);
>
> -       clk_disable_unprepare(msm_port->clk);
> -
>         free_irq(port->irq, port);
>  }
>
> @@ -1451,7 +1440,7 @@ static int __init msm_console_setup(struct console *co, char *options)
>         if (unlikely(!port->membase))
>                 return -ENXIO;
>
> -       msm_init_clock(port);
> +       msm_serial_set_mnd_regs(port);
>
>         if (options)
>                 uart_parse_options(options, &baud, &parity, &bits, &flow);
> --
> 1.8.2.1
>