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From:   Lina Iyer <ilina@codeaurora.org>
To:     agross@kernel.org, bjorn.andersson@linaro.org, swboyd@chromium.org
Cc:     linux-arm-msm@vger.kernel.org, linux-soc@vger.kernel.org,
        rnayak@codeaurora.org, linux-kernel@vger.kernel.org,
        linux-pm@vger.kernel.org, dianders@chromium.org,
        mkshah@codeaurora.org, Lina Iyer <ilina@codeaurora.org>
Subject: [PATCH V2 2/4] drivers: qcom: rpmh-rsc: avoid locking in the interrupt handler
Date:   Mon, 22 Jul 2019 15:53:38 -0600
Message-Id: <20190722215340.3071-2-ilina@codeaurora.org>
In-Reply-To: <20190722215340.3071-1-ilina@codeaurora.org>
References: <20190722215340.3071-1-ilina@codeaurora.org>
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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@codeaurora.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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