cpu: stm32_common: always do gpio_read() from input register

[kaspar030]

Contribution description

Current stm32 gpio_read() returns the value of the output register (ODR), if the pin is configured as output.

According to the datasheet (of stm32f401):

When the I/O port is programmed as Input:
• The data present on the I/O pin are sampled into the input data register every AHB
clock cycle
• A read access to the input data register provides the I/O State

When the I/O port is programmed as output:
• The data present on the I/O pin are sampled into the input data register every AHB
clock cycle
• A read access to the input data register gets the I/O state
• A read access to the output data register gets the last written value

When the I/O port is programmed as alternate function:
• The data present on the I/O pin are sampled into the input data register every AHB
clock cycle
• A read access to the input data register gets the I/O state

Thus the input register always contains the actual pin state. The output register only what was last set, which for alternate functions (PWM) is always 0.

This PR changes the read to always return the pins IDR.

[vincent-d]

Looks legit. And it seems that's how it's implemented in st libraries.

[vincent-d]

ACK

[vincent-d]

Tested on a nucleo144-f413 with example/default. I won't merge now as the request for comments tag as been set, but I'm OK with these changes.

[haukepetersen]

ACK

[haukepetersen]

all green -> go

[kaspar030]

(@haukepetersen and I can't remember why this was implemented as it was before)