linux-kernel - Re: [PATCH] serial: tegra: Fixes lower tolerance baud rate limit for older tegra chips introduced by d781ec21bae6

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Date:   Mon, 29 Nov 2021 15:32:46 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Patrik John <patrik.john@...lox.com>, linux-kernel@...r.kernel.org
Cc:     gregkh@...uxfoundation.org, ldewangan@...dia.com,
        thierry.reding@...il.com, jonathan@...dia.com,
        linux-serial@...r.kernel.org, linux-tegra@...r.kernel.org
Subject: Re: [PATCH] serial: tegra: Fixes lower tolerance baud rate limit for
 older tegra chips introduced by d781ec21bae6

22.11.2021 15:44, Patrik John пишет:
> The current implementation uses 0 as lower limit for the baud rate tolerance which contradicts the initial commit description (https://git.kernel.org/pub/scm/linux/kernel/git/tegra/linux.git/commit/drivers/tty/serial/serial-tegra.c?h=for-next&id=d781ec21bae6ff8f9e07682e8947a654484611f5) of +4/-4% tolerance for older tegra chips other than Tegra186 and Tegra194.
> This causes issues on UART initilization as soon as the actual baud rate clock is slightly lower than required which we have seen on the Tegra124-based Toradex Apalis TK1 which also uses tegra30-hsuart as compatible in the DT serial node (for reference line 1540ff https://git.kernel.org/pub/scm/linux/kernel/git/tegra/linux.git/tree/arch/arm/boot/dts/tegra124-apalis-v1.2.dtsi?h=for-next)
> 
> The standard baud rate tolerance limits are also stated in the tegra20-hsuart driver description (https://www.kernel.org/doc/Documentation/devicetree/bindings/serial/nvidia%2Ctegra20-hsuart.txt).
> 
> The previously introduced check_rate_in_range() always fails due to the lower limit set to 0 even if the actual baud rate is within the required -4% tolerance.
> 
> static int tegra_check_rate_in_range(struct tegra_uart_port *tup)
> {
>     long diff;
>     diff = ((long)(tup->configured_rate - tup->required_rate) * 10000)
>         / tup->required_rate;
>     if (diff < (tup->cdata->error_tolerance_low_range * 100) ||
>         diff > (tup->cdata->error_tolerance_high_range * 100)) {
>         dev_err(tup->uport.dev,
>             "configured baud rate is out of range by %ld", diff);
>         return -EIO;
>     }
>     return 0;
> }
> 
> Changing the lower tolerance limit to the actual -4% resolved the issues for the Tegra124 and should resolve potential issues for other Tegra20/Tegra30 based platforms as well.


Hi,

1. The text of commit message should be wrapped around 75 chars. Please
run "./scripts/checkpatch.pl example.patch" and fix all reported
problems before sending out the patch.

2. This patch should have v2 in the title. Please use the "git
format-patch -v3" next time, it will generate patch with v3 in the title.

3. Use "Link" tag and put all http links here, before the Signed-off-by
tag, like this:

Link:
https://git.kernel.org/pub/scm/linux/kernel/git/tegra/linux.git/commit/drivers/tty/serial/serial-tegra.c?h=for-next&id=d781ec21bae6ff8f9e07682e8947a654484611f5
Link:
https://git.kernel.org/pub/scm/linux/kernel/git/tegra/linux.git/tree/arch/arm/boot/dts/tegra124-apalis-v1.2.dtsi?h=for-next
Link:
https://www.kernel.org/doc/Documentation/devicetree/bindings/serial/nvidia%2Ctegra20-hsuart.txt

> Signed-off-by: Patrik John <patrik.john@...lox.com>
> ---
>  drivers/tty/serial/serial-tegra.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/tty/serial/serial-tegra.c b/drivers/tty/serial/serial-tegra.c
> index 45e2e4109acd..b6223fab0687 100644
> --- a/drivers/tty/serial/serial-tegra.c
> +++ b/drivers/tty/serial/serial-tegra.c
> @@ -1506,7 +1506,7 @@ static struct tegra_uart_chip_data tegra20_uart_chip_data = {
>  	.fifo_mode_enable_status	= false,
>  	.uart_max_port			= 5,
>  	.max_dma_burst_bytes		= 4,
> -	.error_tolerance_low_range	= 0,
> +	.error_tolerance_low_range	= -4,
>  	.error_tolerance_high_range	= 4,
>  };
>  
> @@ -1517,7 +1517,7 @@ static struct tegra_uart_chip_data tegra30_uart_chip_data = {
>  	.fifo_mode_enable_status	= false,
>  	.uart_max_port			= 5,
>  	.max_dma_burst_bytes		= 4,
> -	.error_tolerance_low_range	= 0,
> +	.error_tolerance_low_range	= -4,
>  	.error_tolerance_high_range	= 4,
>  };
>  
>