disable FB

hc

2024-01-04 1543e317f1da31b75942316931e8f491a8920811

 kernel/drivers/tty/serial/8250/8250_dwlib.c
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@@ -80,7 +80,7 @@
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 void dw8250_setup_port(struct uart_port *p)
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 {
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 	struct uart_8250_port *up = up_to_u8250p(p);
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-	u32 reg;
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+	u32 reg, old_dlf;
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 	/*
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 	 * If the Component Version Register returns zero, we know that
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@@ -93,9 +93,11 @@
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 	dev_dbg(p->dev, "Designware UART version %c.%c%c\n",
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 		(reg >> 24) & 0xff, (reg >> 16) & 0xff, (reg >> 8) & 0xff);
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+	/* Preserve value written by firmware or bootloader  */
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+	old_dlf = dw8250_readl_ext(p, DW_UART_DLF);
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 	dw8250_writel_ext(p, DW_UART_DLF, ~0U);
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 	reg = dw8250_readl_ext(p, DW_UART_DLF);
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-	dw8250_writel_ext(p, DW_UART_DLF, 0);
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+	dw8250_writel_ext(p, DW_UART_DLF, old_dlf);
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 	if (reg) {
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 		struct dw8250_port_data *d = p->private_data;