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

From: Dmitry Osipenko
Date: Mon Nov 29 2021 - 08:50:14 EST


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@xxxxxxxxxx>
> ---
> 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,
> };
>
>