linux-kernel - [PATCH V2 2/4] drivers: qcom: rpmh-rsc: avoid locking in the interrupt handler

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Message-Id: <20190722215340.3071-2-ilina@codeaurora.org>
Date:   Mon, 22 Jul 2019 15:53:38 -0600
From:   Lina Iyer <ilina@...eaurora.org>
To:     agross@...nel.org, bjorn.andersson@...aro.org, swboyd@...omium.org
Cc:     linux-arm-msm@...r.kernel.org, linux-soc@...r.kernel.org,
        rnayak@...eaurora.org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, dianders@...omium.org,
        mkshah@...eaurora.org, Lina Iyer <ilina@...eaurora.org>
Subject: [PATCH V2 2/4] drivers: qcom: rpmh-rsc: avoid locking in the interrupt handler

Avoid locking in the interrupt context to improve latency. Since we
don't lock in the interrupt context, it is possible that we now could
race with the DRV_CONTROL register that writes the enable register and
cleared by the interrupt handler. For fire-n-forget requests, the
interrupt may be raised as soon as the TCS is triggered and the IRQ
handler may clear the enable bit before the DRV_CONTROL is read back.

Use the non-sync variant when enabling the TCS register to avoid reading
back a value that may been cleared because the interrupt handler ran
immediately after triggering the TCS.

Signed-off-by: Lina Iyer <ilina@...eaurora.org>
---
 drivers/soc/qcom/rpmh-rsc.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/drivers/soc/qcom/rpmh-rsc.c b/drivers/soc/qcom/rpmh-rsc.c
index 5ede8d6de3ad..694ba881624e 100644
--- a/drivers/soc/qcom/rpmh-rsc.c
+++ b/drivers/soc/qcom/rpmh-rsc.c
@@ -242,9 +242,7 @@ static irqreturn_t tcs_tx_done(int irq, void *p)
 		write_tcs_reg(drv, RSC_DRV_CMD_ENABLE, i, 0);
 		write_tcs_reg(drv, RSC_DRV_CMD_WAIT_FOR_CMPL, i, 0);
 		write_tcs_reg(drv, RSC_DRV_IRQ_CLEAR, 0, BIT(i));
-		spin_lock(&drv->lock);
 		clear_bit(i, drv->tcs_in_use);
-		spin_unlock(&drv->lock);
 		if (req)
 			rpmh_tx_done(req, err);
 	}
@@ -304,7 +302,7 @@ static void __tcs_trigger(struct rsc_drv *drv, int tcs_id)
 	enable = TCS_AMC_MODE_ENABLE;
 	write_tcs_reg_sync(drv, RSC_DRV_CONTROL, tcs_id, enable);
 	enable |= TCS_AMC_MODE_TRIGGER;
-	write_tcs_reg_sync(drv, RSC_DRV_CONTROL, tcs_id, enable);
+	write_tcs_reg(drv, RSC_DRV_CONTROL, tcs_id, enable);
 }
 
 static int check_for_req_inflight(struct rsc_drv *drv, struct tcs_group *tcs,
-- 
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