linux-kernel - Re: [PATCH] serial: msm: Configure correct working mode before starting earlycon

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Message-ID: <ac130f09d89b8efea8e0d24f1465c42f@kernel.org>
Date: Wed, 09 Apr 2025 11:11:00 -0700
From: Stephen Boyd <sboyd@...nel.org>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Jiri Slaby <jirislaby@...nel.org>, Stephan Gerhold <stephan.gerhold@...aro.org>
Cc: linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org, Sam Day <me@...cday.com>
Subject: Re: [PATCH] serial: msm: Configure correct working mode before starting earlycon

Quoting Stephan Gerhold (2025-04-08 10:22:47)
> diff --git a/drivers/tty/serial/msm_serial.c b/drivers/tty/serial/msm_serial.c
> index 1b137e06844425584afe5d3f647e9537c6e2d658..3449945493ceb42369d2acafca925350fccc4f82 100644
> --- a/drivers/tty/serial/msm_serial.c
> +++ b/drivers/tty/serial/msm_serial.c
> @@ -1746,6 +1746,12 @@ msm_serial_early_console_setup_dm(struct earlycon_device *device,
>         if (!device->port.membase)
>                 return -ENODEV;
>  
> +       /* Disable DM / single-character modes */
> +       msm_write(&device->port, 0, UARTDM_DMEN);
> +       msm_write(&device->port, MSM_UART_CR_CMD_RESET_RX, MSM_UART_CR);
> +       msm_write(&device->port, MSM_UART_CR_CMD_RESET_TX, MSM_UART_CR);
> +       msm_write(&device->port, MSM_UART_CR_TX_ENABLE, MSM_UART_CR);

In msm_complete_tx_dma() these are under an if condition checking the
version of uartdm. Do we need that here? Although I also see that
MSM_UART_CR_CMD_RESET_TX is unconditionally written in msm_reset() but
not MSM_UART_CR_TX_ENABLE so maybe the condition check is wrong or the
bit doesn't exist in earlier versions of the hardware so it doesn't
really matter.