linux-kernel - [PATCH v5 2/4] pinctrl: qcom: No need to read-modify-write the interrupt status

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Date:   Fri,  8 Jan 2021 09:35:14 -0800
From:   Douglas Anderson <dianders@...omium.org>
To:     Marc Zyngier <maz@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Linus Walleij <linus.walleij@...aro.org>
Cc:     Bjorn Andersson <bjorn.andersson@...aro.org>,
        Neeraj Upadhyay <neeraju@...eaurora.org>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Maulik Shah <mkshah@...eaurora.org>,
        linux-gpio@...r.kernel.org,
        Srinivas Ramana <sramana@...eaurora.org>,
        linux-arm-msm@...r.kernel.org,
        Douglas Anderson <dianders@...omium.org>,
        Andy Gross <agross@...nel.org>, linux-kernel@...r.kernel.org
Subject: [PATCH v5 2/4] pinctrl: qcom: No need to read-modify-write the interrupt status

When the Qualcomm pinctrl driver wants to Ack an interrupt, it does a
read-modify-write on the interrupt status register.  On some SoCs it
makes sure that the status bit is 1 to "Ack" and on others it makes
sure that the bit is 0 to "Ack".  Presumably the first type of
interrupt controller is a "write 1 to clear" type register and the
second just let you directly set the interrupt status register.

As far as I can tell from scanning structure definitions, the
interrupt status bit is always in a register by itself.  Thus with
both types of interrupt controllers it is safe to "Ack" interrupts
without doing a read-modify-write.  We can do a simple write.

It should be noted that if the interrupt status bit _was_ ever in a
register with other things (like maybe status bits for other GPIOs):
a) For "write 1 clear" type controllers then read-modify-write would
   be totally wrong because we'd accidentally end up clearing
   interrupts we weren't looking at.
b) For "direct set" type controllers then read-modify-write would also
   be wrong because someone setting one of the other bits in the
   register might accidentally clear (or set) our interrupt.
I say this simply to show that the current read-modify-write doesn't
provide any sort of "future proofing" of the code.  In fact (for
"write 1 clear" controllers) the new code is slightly more "future
proof" since it would allow more than one interrupt status bits to
share a register.

NOTE: this code fixes no bugs--it simply avoids an extra register
read.

Signed-off-by: Douglas Anderson <dianders@...omium.org>
---

Changes in v5:
- ("pinctrl: qcom: No need to read-modify-write the ...") new for v5.

 drivers/pinctrl/qcom/pinctrl-msm.c | 23 ++++++++---------------
 1 file changed, 8 insertions(+), 15 deletions(-)

diff --git a/drivers/pinctrl/qcom/pinctrl-msm.c b/drivers/pinctrl/qcom/pinctrl-msm.c
index 1d2a78452c2d..1787ada6bfab 100644
--- a/drivers/pinctrl/qcom/pinctrl-msm.c
+++ b/drivers/pinctrl/qcom/pinctrl-msm.c
@@ -792,16 +792,13 @@ static void msm_gpio_irq_clear_unmask(struct irq_data *d, bool status_clear)

 	raw_spin_lock_irqsave(&pctrl->lock, flags);

-	if (status_clear) {
-		/*
-		 * clear the interrupt status bit before unmask to avoid
-		 * any erroneous interrupts that would have got latched
-		 * when the interrupt is not in use.
-		 */
-		val = msm_readl_intr_status(pctrl, g);
-		val &= ~BIT(g->intr_status_bit);
-		msm_writel_intr_status(val, pctrl, g);
-	}
+	/*
+	 * clear the interrupt status bit before unmask to avoid
+	 * any erroneous interrupts that would have got latched
+	 * when the interrupt is not in use.
+	 */
+	if (status_clear)
+		msm_writel_intr_status(0, pctrl, g);

 	val = msm_readl_intr_cfg(pctrl, g);
 	val |= BIT(g->intr_raw_status_bit);
@@ -906,11 +903,7 @@ static void msm_gpio_irq_ack(struct irq_data *d)

 	raw_spin_lock_irqsave(&pctrl->lock, flags);

-	val = msm_readl_intr_status(pctrl, g);
-	if (g->intr_ack_high)
-		val |= BIT(g->intr_status_bit);
-	else
-		val &= ~BIT(g->intr_status_bit);
+	val = (g->intr_ack_high) ? BIT(g->intr_status_bit) : 0;
 	msm_writel_intr_status(val, pctrl, g);

 	if (test_bit(d->hwirq, pctrl->dual_edge_irqs))
-- 
2.29.2.729.g45daf8777d-goog