linux-kernel - [PATCH v3] serial: tegra: Change lower tolerance baud rate limit for tegra20 and tegra30

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Message-Id: <sig.19614244f8.20211123132737.88341-1-patrik.john@u-blox.com>
Date:   Tue, 23 Nov 2021 14:27:38 +0100
From:   Patrik John <patrik.john@...lox.com>
To:     <linux-kernel@...r.kernel.org>
CC:     <gregkh@...uxfoundation.org>, <ldewangan@...dia.com>,
        <thierry.reding@...il.com>, <jonathanh@...dia.com>,
        <linux-serial@...r.kernel.org>, <linux-tegra@...r.kernel.org>,
        Patrik John <patrik.john@...lox.com>
Subject: [PATCH v3] serial: tegra: Change lower tolerance baud rate limit for tegra20 and tegra30

The current implementation uses 0 as lower limit for the baud rate
tolerance for tegra20 and tegra30 chips which causes isses on UART
initialization as soon as baud rate clock is lower than required even
when within the standard UART tolerance of +/- 4%.

This fix aligns the implementation with the initial commit description
of +/- 4% tolerance for tegra chips other than tegra186 and
tegra194.

Fixes: d781ec21bae6 ("serial: tegra: report clk rate errors")
Signed-off-by: Patrik John <patrik.john@...lox.com>
---
This issue has been present since 5.4-rc1 and is applicable
to 5.4.y and 5.10.y longterm releases as well. 

Changes in v3:
- Changed Subject to be more precise
- Reworked commit message to meet guidelines
- Added Patch versions
Changes in v2:
- Fixed errors reported by Greg's bot  
 
 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,
 };
 
-- 
2.25.1