FDC2x1x driver contains critical memory access issues

[TylerBird]

Describe the bug

I wanted to use the TI sensor fdc2x1x (onboard I have a FDC2214). The driver is also available. After integration, the controller did not start and I received a “fatal exception” error.

First, I had an ESP32 (board: M5StickC-plus, flashed via UART), then I tried it with an STM32L552 (flashed via STLink V3) controller.

After ruling out the app code as the source of the error, I took a look at the driver. Here I discovered memory access violations.
For example, here:
Note the variable access cfg->ch_cfg->fin_sel which is channel specific and therefore must be implemented as follows: cfg->ch_cfg-[ch].fin_sel.

I have noticed 3 of these access violations.

Furthermore, I use the chip without the sd_gpio.
In the code, however, the function fdc2x1x_init(const struct device *dev) incorrectly checks whether this has been set in the device tree.

Here is what helped me:
if (cfg->sd_gpio.port->name) { -> if (cfg->sd_gpio.port) {

Regression

• This is a regression.

Steps to reproduce

Execute the example from the folder samples/sensor/fdc2x1x.

Relevant log output

Impact

Annoyance – Minor irritation; no significant impact on usability or functionality.

Environment

• Linux Ubuntu
• Zephyr SDK with VSCode
• zephyrproject-rtos with revision: v4.1.0-rc3

Additional Context

No response

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[TylerBird]

The driver appears to be correct.

The original issue I had was that I did not defined the SD pin in the device tree.
Based on the documentation (https://docs.zephyrproject.org/latest/build/dts/api/bindings/sensor/ti%2Cfdc2x1x.html) for sd-gpio, where it does not say “This property is required” I assume that I do not need to specify the pin.

In my case, I set the SD pin in the hardware to “always active” using a pull-down resistor. So the pin is not connected to my controller.

[NotAnsgar]

I checked the sensor readings, and they’re correct when an sd-gpio is provided; the documentation doesn’t list it as mandatory.

When sd-gpio isn’t specified, Zephyr raises an EXCEPTION.

While debugging the initialization I found that sd_gpio is NULL, so dereferencing its name member triggers the exception.

A straightforward fix is to replace
if (cfg->sd_gpio.port->name) {

with

if (cfg->sd_gpio.port) {.

After this change, the FDC2214 can be read both with and without an sd-gpio in the device tree and the fdc2x1x_init_sd_pin(dev) will only be called if the sd-gpio is specified.

I’m not certain whether this will later interfere with power-management routines that use the pin to shut down the FDC, but the adjustment probably best matches the driver author’s intent.

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