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serial: sh-sci: Reorder the SCxTDR write after the TDxE clear.

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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>
This commit is contained in:
Paul Mundt 2008-11-13 17:46:06 +09:00
parent 5d52013cbb
commit 272966c070
2 changed files with 2 additions and 2 deletions
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2
arch/sh/kernel/early_printk.c
View File

@ -85,9 +85,9 @@ static void scif_sercon_putc(int c)
while (((sci_in(&scif_port, SCFDR) & EPK_FIFO_BITS) >= EPK_FIFO_SIZE)) while (((sci_in(&scif_port, SCFDR) & EPK_FIFO_BITS) >= EPK_FIFO_SIZE))
; ;
sci_out(&scif_port, SCxTDR, c);
sci_in(&scif_port, SCxSR); sci_in(&scif_port, SCxSR);
sci_out(&scif_port, SCxSR, 0xf3 & ~(0x20 | 0x40)); sci_out(&scif_port, SCxSR, 0xf3 & ~(0x20 | 0x40));
sci_out(&scif_port, SCxTDR, c);
while ((sci_in(&scif_port, SCxSR) & 0x40) == 0) while ((sci_in(&scif_port, SCxSR) & 0x40) == 0)
; ;

2
drivers/serial/sh-sci.c
View File

@ -144,9 +144,9 @@ static void put_char(struct uart_port *port, char c)
status = sci_in(port, SCxSR); status = sci_in(port, SCxSR);
} while (!(status & SCxSR_TDxE(port))); } while (!(status & SCxSR_TDxE(port)));
sci_out(port, SCxTDR, c);
sci_in(port, SCxSR); /* Dummy read */ sci_in(port, SCxSR); /* Dummy read */
sci_out(port, SCxSR, SCxSR_TDxE_CLEAR(port)); sci_out(port, SCxSR, SCxSR_TDxE_CLEAR(port));
sci_out(port, SCxTDR, c);
spin_unlock_irqrestore(&port->lock, flags); spin_unlock_irqrestore(&port->lock, flags);
} }