Subject: Re: [PATCH] serial: tegra: Fixes lower tolerance baud rate limit for
 older tegra chips introduced by d781ec21bae6
To:     =?UTF-8?B?TWljaGHFgiBNaXJvc8WCYXc=?= <mirq-linux@rere.qmqm.pl>,
        Patrik John <patrik.john@u-blox.com>
Cc:     linux-kernel@vger.kernel.org, gregkh@linuxfoundation.org,
        ldewangan@nvidia.com, thierry.reding@gmail.com,
        jonathan@nvidia.com, linux-serial@vger.kernel.org,
        linux-tegra@vger.kernel.org
References: <sig.096060f39c.20211122124425.74031-1-patrik.john@u-blox.com>
 <YaK9DwsgGr8eaMuX@qmqm.qmqm.pl>
From:   Dmitry Osipenko <digetx@gmail.com>
Message-ID: <7242bcd6-bb40-dc21-31b9-051429b89122@gmail.com>
Date:   Mon, 29 Nov 2021 15:33:56 +0300
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28.11.2021 02:19, Michał Mirosław пишет:
> 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)
>>
>> 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.
>>
> [...]
> 
> I have a same patch waiting in my tree [1]. Feel free to use the commit
> message and to add:
> 
> Reviewed-and-tested-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
> 
> [1] https://rere.qmqm.pl/git/?p=linux;a=commitdiff;h=b658dcd83d0db777410fe960721193d35a38115a

The Reviewed-and-tested-by isn't a valid tag, should be two separate tags:

Reviewed-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Tested-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>