On Mon, Nov 22, 2021 at 01:44:26PM +0100, Patrik John wrote:

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)

All of these links will break in a few days.

And a line number is not "1540ff" :(

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).

You can just reference a file in the kernel source tree directly, no
need to go back to kernel.org

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.

Can you please wrap your changelog text at 72 columns like git asked you
to when you committed the change to your local tree?

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;
}

I do not understand, why is this code in the changelog?

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.

Signed-off-by: Patrik John <redacted>

What commit does this fix?  Should it have a "Fixes:" tag in it?

And should it go to stable kernel(s)?

Also, this is a v2 patch, please include below the --- line what changed
from the previous version when you resend v3.

thanks,

greg k-h