linux-kernel - [RFT PATCH 6/9] drivers: qcom: rpmh-rsc: Only use "tcs_in_use" for ACTIVE

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Date:   Fri,  6 Mar 2020 15:59:48 -0800
From:   Douglas Anderson <dianders@...omium.org>
To:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Maulik Shah <mkshah@...eaurora.org>
Cc:     Rajendra Nayak <rnayak@...eaurora.org>, mka@...omium.org,
        evgreen@...omium.org, swboyd@...omium.org,
        Lina Iyer <ilina@...eaurora.org>,
        Douglas Anderson <dianders@...omium.org>,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [RFT PATCH 6/9] drivers: qcom: rpmh-rsc: Only use "tcs_in_use" for ACTIVE_ONLY

>From trawling through the code (see the "A lot of comments" change) I
found that "tcs_in_use" was only kept up-to-date for ACTIVE_ONLY TCSs.
...yet tcs_is_free() was checking the variable called from
tcs_invalidate() and tcs_invalidate() is only used for non-ACTIVE_ONLY
TCSs.

Let's change tcs_invalidate() to just check the "RSC_DRV_STATUS"
register, which was presumably the important part.

It also feels like for ACTIVE_ONLY TCSs that it probably wasn't
important to check the "RSC_DRV_STATUS".  We'll keep doing it just in
case but we'll add a warning if it ever actually mattered.

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

 drivers/soc/qcom/rpmh-rsc.c | 23 +++++++++++++++++++----
 1 file changed, 19 insertions(+), 4 deletions(-)

diff --git a/drivers/soc/qcom/rpmh-rsc.c b/drivers/soc/qcom/rpmh-rsc.c
index 190226151029..c63441182358 100644
--- a/drivers/soc/qcom/rpmh-rsc.c
+++ b/drivers/soc/qcom/rpmh-rsc.c
@@ -164,7 +164,7 @@ static void write_tcs_reg_sync(struct rsc_drv *drv, int reg, int tcs_id,
 }
 
 /**
- * tcs_is_free() - Return if a TCS is totally free.
+ * tcs_is_free() - Return if an ACTIVE_ONLY TCS is totally free.
  * @drv:    The RSC controller.
  * @tcs_id: The global ID of this TCS.
  *
@@ -177,8 +177,23 @@ static void write_tcs_reg_sync(struct rsc_drv *drv, int reg, int tcs_id,
  */
 static bool tcs_is_free(struct rsc_drv *drv, int tcs_id)
 {
-	return !test_bit(tcs_id, drv->tcs_in_use) &&
-	       read_tcs_reg(drv, RSC_DRV_STATUS, tcs_id);
+	if (test_bit(tcs_id, drv->tcs_in_use))
+		return false;
+
+	if (read_tcs_reg(drv, RSC_DRV_STATUS, tcs_id) != 0)
+		return true;
+
+	/*
+	 * If this warning never ever hits then we can change this function
+	 * to just look at "tcs_in_use" and skip the read of the
+	 * RSC_DRV_STATUS register.
+	 *
+	 * If this warning _does_ hit, we should figure out if this is just
+	 * the way the hardware works or if there is some bug being pointed
+	 * out.
+	 */
+	WARN(1, "Driver thought TCS was free but HW reported busy\n");
+	return false;
 }
 
 /**
@@ -204,7 +219,7 @@ static int tcs_invalidate(struct rsc_drv *drv, int type)
 	}
 
 	for (m = tcs->offset; m < tcs->offset + tcs->num_tcs; m++) {
-		if (!tcs_is_free(drv, m)) {
+		if (read_tcs_reg(drv, RSC_DRV_STATUS, m) == 0) {
 			spin_unlock(&tcs->lock);
 			return -EAGAIN;
 		}
-- 
2.25.1.481.gfbce0eb801-goog