linux-kernel - [PATCH] irqchip: vt8500: Switch to a simple write clear for Interrupt Status Register

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Date:	Sun, 27 Apr 2014 23:13:47 +0800
From:	Axel Lin <axel.lin@...ics.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Tony Prisk <linux@...sktech.co.nz>, linux-kernel@...r.kernel.org
Subject: [PATCH] irqchip: vt8500: Switch to a simple write clear for
 Interrupt Status Register

According to the datasheet, the attribute of Interrupt Status Register is RW0S,
which means:
	Software can read the register.
	Software can also "write 1 to clear". "write 0" has no effect.
Thus switch the read/modify/write to a simple write clear.

A read/modify/write does not make sense for an irq status register like this,
since otherwise a read/modify/write can race with a device raising an interrupt
and then clear the pending bit unintentionally.

Signed-off-by: Axel Lin <axel.lin@...ics.com>
---
Hi Tony,
I don't have this h/w to test, I'd appreciate if you can review and test this
patch.

Regards,
Axel

 drivers/irqchip/irq-vt8500.c | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/drivers/irqchip/irq-vt8500.c b/drivers/irqchip/irq-vt8500.c
index eb6e91e..a0085bc 100644
--- a/drivers/irqchip/irq-vt8500.c
+++ b/drivers/irqchip/irq-vt8500.c
@@ -87,14 +87,10 @@ static void vt8500_irq_mask(struct irq_data *d)
 	void __iomem *base = priv->base;
 	void __iomem *stat_reg = base + VT8500_ICIS + (d->hwirq < 32 ? 0 : 4);
 	u8 edge, dctr;
-	u32 status;
 
 	edge = readb(base + VT8500_ICDC + d->hwirq) & VT8500_EDGE;
 	if (edge) {
-		status = readl(stat_reg);
-
-		status |= (1 << (d->hwirq & 0x1f));
-		writel(status, stat_reg);
+		writel(BIT(d->hwirq & 0x1f), stat_reg);
 	} else {
 		dctr = readb(base + VT8500_ICDC + d->hwirq);
 		dctr &= ~VT8500_INT_ENABLE;
-- 
1.8.3.2



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