[bootlin/training-materials updates] master: kernel: serial-iomem: (8c5aa689)
Miquel Raynal
miquel.raynal at bootlin.com
Mon Jul 12 20:16:42 CEST 2021
Repository : https://github.com/bootlin/training-materials
On branch : master
Link : https://github.com/bootlin/training-materials/commit/8c5aa689f684c998159e7af4d37d27aa15177c85
>---------------------------------------------------------------
commit 8c5aa689f684c998159e7af4d37d27aa15177c85
Author: Miquel Raynal <miquel.raynal at bootlin.com>
Date: Mon Jul 12 20:16:40 2021 +0200
kernel: serial-iomem:
Assuming TTL UART, the Tx line is an output and the Rx line is an input:
* The Rx line must remain stable at a high logic level if the other end
gets disconnected, hence the use of a an internal pull-up makes
totally sense.
* However, while configured in UART mode, the Tx line will be driven, so
we don't really care about setting an internal pull-up or pull-down.
The current pull-down configuration was copy-pasted from other device
trees, which probably were also copy-pasted from the work of a single
person which only focused on the fact that it worked configured like
this (and it does, the additional wired resistor does nothing on a
driven output). So let's get rid of it.
Signed-off-by: Miquel Raynal <miquel.raynal at bootlin.com>
>---------------------------------------------------------------
8c5aa689f684c998159e7af4d37d27aa15177c85
labs/kernel-serial-iomem/kernel-serial-iomem.tex | 5 +----
labs/kernel-serial-iomem/uarts-pinctrl.dts | 4 ++--
2 files changed, 3 insertions(+), 6 deletions(-)
diff --git a/labs/kernel-serial-iomem/kernel-serial-iomem.tex b/labs/kernel-serial-iomem/kernel-serial-iomem.tex
index 5224ef89..83d80e50 100644
--- a/labs/kernel-serial-iomem/kernel-serial-iomem.tex
+++ b/labs/kernel-serial-iomem/kernel-serial-iomem.tex
@@ -47,10 +47,7 @@ as for the cable that you're using for the console:
Now, create again a new
\code{arch/arm/boot/dts/am335x-customboneblack.dts} file including
the standard board DTS file and create a pin muxing section with
-declarations for UART2 and UART4 (took the below definitions from
-\kfile{arch/arm/boot/dts/am335x-boneblue.dts} and
-\kfile{arch/arm/boot/dts/am335x-pocketbeagle.dts}, sharing the same
-SoC):
+declarations for UART2 and UART4.
{\scriptsize \sourcecode{labs/kernel-serial-iomem/uarts-pinctrl.dts}}
diff --git a/labs/kernel-serial-iomem/uarts-pinctrl.dts b/labs/kernel-serial-iomem/uarts-pinctrl.dts
index 2837d55f..6f658f59 100644
--- a/labs/kernel-serial-iomem/uarts-pinctrl.dts
+++ b/labs/kernel-serial-iomem/uarts-pinctrl.dts
@@ -4,7 +4,7 @@ uart2_pins: uart2_pins {
/* (A17) spi0_sclk.uart2_rxd */
AM33XX_PADCONF(AM335X_PIN_SPI0_SCLK, PIN_INPUT_PULLUP, MUX_MODE1)
/* (B17) spi0_d0.uart2_txd */
- AM33XX_PADCONF(AM335X_PIN_SPI0_D0, PIN_OUTPUT_PULLDOWN, MUX_MODE1)
+ AM33XX_PADCONF(AM335X_PIN_SPI0_D0, PIN_OUTPUT, MUX_MODE1)
>;
};
@@ -14,6 +14,6 @@ uart4_pins: uart4_pins {
/* (T17) gpmc_wait0.uart4_rxd */
AM33XX_PADCONF(AM335X_PIN_GPMC_WAIT0, PIN_INPUT_PULLUP, MUX_MODE6)
/* (U17) gpmc_wpn.uart4_txd */
- AM33XX_PADCONF(AM335X_PIN_GPMC_WPN, PIN_OUTPUT_PULLDOWN, MUX_MODE6)
+ AM33XX_PADCONF(AM335X_PIN_GPMC_WPN, PIN_OUTPUT, MUX_MODE6)
>;
};
More information about the training-materials-updates
mailing list