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serial: 8250: Store to lsr_save_flags after lsr read
Not all LSR register flags are preserved across reads. Therefore, LSR readers must store the non-preserved bits into lsr_save_flags. This fix was initially mixed into feature commitf6f586102a
("serial: 8250: Handle UART without interrupt on TEMT using em485"). However, that feature change had a flaw and it was reverted to make room for simpler approach providing the same feature. The embedded fix got reverted with the feature change. Re-add the lsr_save_flags fix and properly mark it's a fix. Link: https://lore.kernel.org/all/1d6c31d-d194-9e6a-ddf9-5f29af829f3@linux.intel.com/T/#m1737eef986bd20cf19593e344cebd7b0244945fc Fixes:e490c9144c
("tty: Add software emulated RS485 support for 8250") Co-developed-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de> Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com> Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com> Link: https://lore.kernel.org/r/20220608095431.18376-2-ilpo.jarvinen@linux.intel.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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@ -1511,6 +1511,8 @@ static inline void __stop_tx(struct uart_8250_port *p)
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unsigned char lsr = serial_in(p, UART_LSR);
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u64 stop_delay = 0;
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p->lsr_saved_flags |= lsr & LSR_SAVE_FLAGS;
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if (!(lsr & UART_LSR_THRE))
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return;
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/*
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