[bootlin/training-materials updates] master: kernel: serial-iomem: (8c5aa689)

[Miquel Raynal]

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>


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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)
 	>;
 };