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Revert "serial: stm32: Give H/W a chance to set the TXE bit on transfer"

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Don't busy-wait in uart_stm32_fifo_fill(), this routine is supposed
to be called on IRQ, and the waiting loop was shown to interfere
with interrupt-driven UART handling.

The original problem mentioned in the patch being reverted ("it is
possible to evaluate the TXE bit *before* H/W has had the
opportunity to detect that data is being processed") may still
exist and may require handling in a different way. The most obvious
way is to replace "while" loop with "if", because STM32 doesn't
have multi-level FIFO anyway. But I was dissuaded to include such a
change as part of this patch, so it's left for future analysis.

This reverts commit 49c2858d94.

Change-Id: Ib27b53ba3a29b84c1a2dccff6d33f4118680cc19
Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>
This commit is contained in:
Paul Sokolovsky 2017-04-24 13:58:21 +03:00 • committed by Kumar Gala
commit abf284e9fd
1 changed files with 0 additions and 7 deletions
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7
drivers/serial/uart_stm32.c
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@ -95,13 +95,6 @@ static int uart_stm32_fifo_fill(struct device *dev, const u8_t *tx_data,
#else
LL_USART_TransmitData8(UartHandle->Instance, tx_data[num_tx++]);
#endif
/*
* Wait for H/W to set TXE flag, or else it will be evaluated
* again at the top of this loop *before* H/W has chance to
* initially detect that data is being processed.
*/
while (!__HAL_UART_GET_FLAG(UartHandle, UART_FLAG_TXE))
;
}
return num_tx;