linux-kernel - [PATCH v3 2/3] bus: sunxi-rsb: Support atomic transfers

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Message-Id: <20221114015749.28490-3-samuel@sholland.org>
Date:   Sun, 13 Nov 2022 19:57:48 -0600
From:   Samuel Holland <samuel@...lland.org>
To:     Chen-Yu Tsai <wens@...e.org>,
        Jernej Skrabec <jernej.skrabec@...il.com>
Cc:     Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-sunxi@...ts.linux.dev,
        Andre Przywara <andre.przywara@....com>,
        Samuel Holland <samuel@...lland.org>
Subject: [PATCH v3 2/3] bus: sunxi-rsb: Support atomic transfers

When communicating with a PMIC during system poweroff (pm_power_off()),
IRQs are disabled and we are in a RCU read-side critical section, so we
cannot use wait_for_completion_io_timeout(). Instead, poll the status
register for transfer completion.

Fixes: d787dcdb9c8f ("bus: sunxi-rsb: Add driver for Allwinner Reduced Serial Bus")
Signed-off-by: Samuel Holland <samuel@...lland.org>
---

Changes in v3:
 - Clear the interrupt status register after polling

Changes in v2:
 - Add Fixes tag to patch 2
 - Only check for specific status bits when polling

 drivers/bus/sunxi-rsb.c | 29 +++++++++++++++++++++--------
 1 file changed, 21 insertions(+), 8 deletions(-)

diff --git a/drivers/bus/sunxi-rsb.c b/drivers/bus/sunxi-rsb.c
index 17343cd75338..3aa91aed3bf7 100644
--- a/drivers/bus/sunxi-rsb.c
+++ b/drivers/bus/sunxi-rsb.c
@@ -267,6 +267,9 @@ EXPORT_SYMBOL_GPL(sunxi_rsb_driver_register);
 /* common code that starts a transfer */
 static int _sunxi_rsb_run_xfer(struct sunxi_rsb *rsb)
 {
+	u32 int_mask, status;
+	bool timeout;
+
 	if (readl(rsb->regs + RSB_CTRL) & RSB_CTRL_START_TRANS) {
 		dev_dbg(rsb->dev, "RSB transfer still in progress\n");
 		return -EBUSY;
@@ -274,13 +277,23 @@ static int _sunxi_rsb_run_xfer(struct sunxi_rsb *rsb)
 
 	reinit_completion(&rsb->complete);
 
-	writel(RSB_INTS_LOAD_BSY | RSB_INTS_TRANS_ERR | RSB_INTS_TRANS_OVER,
-	       rsb->regs + RSB_INTE);
+	int_mask = RSB_INTS_LOAD_BSY | RSB_INTS_TRANS_ERR | RSB_INTS_TRANS_OVER;
+	writel(int_mask, rsb->regs + RSB_INTE);
 	writel(RSB_CTRL_START_TRANS | RSB_CTRL_GLOBAL_INT_ENB,
 	       rsb->regs + RSB_CTRL);
 
-	if (!wait_for_completion_io_timeout(&rsb->complete,
-					    msecs_to_jiffies(100))) {
+	if (irqs_disabled()) {
+		timeout = readl_poll_timeout_atomic(rsb->regs + RSB_INTS,
+						    status, (status & int_mask),
+						    10, 100000);
+		writel(status, rsb->regs + RSB_INTS);
+	} else {
+		timeout = !wait_for_completion_io_timeout(&rsb->complete,
+							  msecs_to_jiffies(100));
+		status = rsb->status;
+	}
+
+	if (timeout) {
 		dev_dbg(rsb->dev, "RSB timeout\n");
 
 		/* abort the transfer */
@@ -292,18 +305,18 @@ static int _sunxi_rsb_run_xfer(struct sunxi_rsb *rsb)
 		return -ETIMEDOUT;
 	}
 
-	if (rsb->status & RSB_INTS_LOAD_BSY) {
+	if (status & RSB_INTS_LOAD_BSY) {
 		dev_dbg(rsb->dev, "RSB busy\n");
 		return -EBUSY;
 	}
 
-	if (rsb->status & RSB_INTS_TRANS_ERR) {
-		if (rsb->status & RSB_INTS_TRANS_ERR_ACK) {
+	if (status & RSB_INTS_TRANS_ERR) {
+		if (status & RSB_INTS_TRANS_ERR_ACK) {
 			dev_dbg(rsb->dev, "RSB slave nack\n");
 			return -EINVAL;
 		}
 
-		if (rsb->status & RSB_INTS_TRANS_ERR_DATA) {
+		if (status & RSB_INTS_TRANS_ERR_DATA) {
 			dev_dbg(rsb->dev, "RSB transfer data error\n");
 			return -EIO;
 		}
-- 
2.37.3