linux-kernel - [PATCH] soc: qcom: rpmh-rsc: Don't use ktime for timeout in write_tcs_reg

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Date:   Thu, 28 May 2020 07:48:34 -0700
From:   Douglas Anderson <dianders@...omium.org>
To:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Maulik Shah <mkshah@...eaurora.org>,
        Douglas Anderson <dianders@...omium.org>,
        Stephen Boyd <swboyd@...omium.org>,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] soc: qcom: rpmh-rsc: Don't use ktime for timeout in write_tcs_reg_sync()

The write_tcs_reg_sync() may be called after timekeeping is suspended
so it's not OK to use ktime.  The readl_poll_timeout_atomic() macro
implicitly uses ktime.  This was causing a warning at suspend time.

Change to just loop 1000000 times with a delay of 1 us between loops.
This may give a timeout of more than 1 second but never less and is
safe even if timekeeping is suspended.

NOTE: I don't have any actual evidence that we need to loop here.
It's possibly that all we really need to do is just read the value
back to ensure that the pipes are cleaned and the looping/comparing is
totally not needed.  I never saw the loop being needed in my tests.
However, the loop shouldn't hurt.

Fixes: 91160150aba0 ("soc: qcom: rpmh-rsc: Timeout after 1 second in write_tcs_reg_sync()")
Reported-by: Maulik Shah <mkshah@...eaurora.org>
Signed-off-by: Douglas Anderson <dianders@...omium.org>
---

 drivers/soc/qcom/rpmh-rsc.c | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/drivers/soc/qcom/rpmh-rsc.c b/drivers/soc/qcom/rpmh-rsc.c
index 076fd27f3081..906778e2c1fa 100644
--- a/drivers/soc/qcom/rpmh-rsc.c
+++ b/drivers/soc/qcom/rpmh-rsc.c
@@ -175,13 +175,21 @@ static void write_tcs_reg(const struct rsc_drv *drv, int reg, int tcs_id,
 static void write_tcs_reg_sync(const struct rsc_drv *drv, int reg, int tcs_id,
 			       u32 data)
 {
-	u32 new_data;
+	int i;
 
 	writel(data, tcs_reg_addr(drv, reg, tcs_id));
-	if (readl_poll_timeout_atomic(tcs_reg_addr(drv, reg, tcs_id), new_data,
-				      new_data == data, 1, USEC_PER_SEC))
-		pr_err("%s: error writing %#x to %d:%#x\n", drv->name,
-		       data, tcs_id, reg);
+
+	/*
+	 * Wait until we read back the same value.  Use a counter rather than
+	 * ktime for timeout since this may be called after timekeeping stops.
+	 */
+	for (i = 0; i < USEC_PER_SEC; i++) {
+		if (readl(tcs_reg_addr(drv, reg, tcs_id)) == data)
+			return;
+		udelay(1);
+	}
+	pr_err("%s: error writing %#x to %d:%#x\n", drv->name,
+	       data, tcs_id, reg);
 }
 
 /**
-- 
2.27.0.rc0.183.gde8f92d652-goog