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drivers: serial: pl011: Remove busy wait in Ambiq UART initiate

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Ambiq UART requires specific busy wait during initialization for
propagating powering control registers, original k_busy_wait()
used here generated a dead loop because k_busy_wait() relays on
timer, who's driver is initialized after UART(UART init in
PRE_KERNEL_1, timer init in PRE_KERNEL_2), replace k_busy_wait()
with checking power status register is more suitable here.

Signed-off-by: Bryan Zhu <bzhu@ambiq.com>
This commit is contained in:
Bryan Zhu 2023-12-08 16:31:29 +08:00 • committed by Carles Cufí
commit 3e456e8cfb
1 changed files with 8 additions and 4 deletions
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12
drivers/serial/uart_pl011_ambiq.h
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@ -50,9 +50,9 @@ static inline int clk_enable_ambiq_uart(const struct device *dev, uint32_t clk)
return pl011_ambiq_clk_set(dev, clk);
}
/* Problem: writes to pwrcfg reg take at most PWCTRL_MAX_WAIT_US time to propagate.
* Solution: busy wait for PWCTRL_MAX_WAIT_US microseconds to ensure that register
* writes have propagated.
/* Problem: writes to power configure register takes some time to take effective.
* Solution: Check device's power status to ensure that register has taken effective.
* Note: busy wait is not allowed to use here due to UART is initiated before timer starts.
*/
#define QUIRK_AMBIQ_UART_DEFINE(n) \
@ -60,8 +60,12 @@ static inline int clk_enable_ambiq_uart(const struct device *dev, uint32_t clk)
{ \
uint32_t addr = DT_REG_ADDR(DT_INST_PHANDLE(n, ambiq_pwrcfg)) + \
DT_INST_PHA(n, ambiq_pwrcfg, offset); \
uint32_t pwr_status_addr = addr + 4; \
sys_write32((sys_read32(addr) | DT_INST_PHA(n, ambiq_pwrcfg, mask)), addr); \
k_busy_wait(PWRCTRL_MAX_WAIT_US); \
while ((sys_read32(pwr_status_addr) & DT_INST_PHA(n, ambiq_pwrcfg, mask)) != \
DT_INST_PHA(n, ambiq_pwrcfg, mask)) { \
arch_nop(); \
}; \
return 0; \
}