serial: sh-sci: Reorder the SCxTDR write after the TDxE clear. (272966c0) · Commits · 戴 / test

Under qemu there is a race between the TDxE read-and-clear and the SCxTDR write. While on hardware it can be gauranteed that the read-and-clear will happen prior to the character being written out, no such assumption can be made under emulation. As this path happens with IRQs off and the hardware itself doesn't care about the ordering, move the SCxTDR write until after the read-and-clear. Signed-off-by:

Vladimir Prus <vladimir@codesourcery.com> Signed-off-by:

Paul Mundt <lethal@linux-sh.org>

arch/sh/kernel/early_printk.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -85,9 +85,9 @@ static void scif_sercon_putc(int c)
		while (((sci_in(&scif_port, SCFDR) & EPK_FIFO_BITS) >= EPK_FIFO_SIZE))
		;

		sci_out(&scif_port, SCxTDR, c);
		sci_in(&scif_port, SCxSR);
		sci_out(&scif_port, SCxSR, 0xf3 & ~(0x20 \| 0x40));
		sci_out(&scif_port, SCxTDR, c);

		while ((sci_in(&scif_port, SCxSR) & 0x40) == 0)
		;

drivers/serial/sh-sci.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -144,9 +144,9 @@ static void put_char(struct uart_port *port, char c)
		status = sci_in(port, SCxSR);
		} while (!(status & SCxSR_TDxE(port)));

		sci_out(port, SCxTDR, c);
		sci_in(port, SCxSR); /* Dummy read */
		sci_out(port, SCxSR, SCxSR_TDxE_CLEAR(port));
		sci_out(port, SCxTDR, c);

		spin_unlock_irqrestore(&port->lock, flags);
		}

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