drivers: clk: stm32h7: Endless loop of dead in driver probe function

["Johannes (krjdev) Krottmayer" <krjdev@gmail.com>]

Hi,

Some IMHO fatal issues in the the clock driver for the
STM32H7 series driver.

Affected driver:
drivers/clk/clk_stm32h7.c

Affected configs (boards):
configs/stm32h750-art-pi_defconfig
configs/stm32h743-disco_defconfig
configs/stm32h743-eval_defconfig

Description:
The driver currently requires a external working clock source
(HSE). No issues in the circuit are accepted by the current
implementation. Also a fixed (defined) frequency of the external
clock source.

In the probe function stm32_clk_probe() from the driver there
will be configure_clocks() called. Here are the issues.

As code snippet from configure_clocks():

/* Switch on HSE */
setbits_le32(&regs->cr, RCC_CR_HSEON);
while (!(readl(&regs->cr) & RCC_CR_HSERDY))
	;

RCC_CR_HSERDY will here never set, when there is no external
clock source or an issue in the circuit. -> Endless loop of dead.

My possible fixes:
At a timeout when reading the register and if the timeout is
elapsed, print an error message and return with ETIMEDOUT, so
the dm manger can call the hang() function.

Johannes K.