linux-kernel - [PATCH 3.16 132/212] clk: renesas: mstp: ensure register writes complete

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Date:   Thu, 01 Jun 2017 16:43:16 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "Geert Uytterhoeven" <geert+renesas@...der.be>,
        "Stephen Boyd" <sboyd@...eaurora.org>,
        "Chris Brandt" <chris.brandt@...esas.com>
Subject: [PATCH 3.16 132/212] clk: renesas: mstp: ensure register writes
 complete

3.16.44-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Chris Brandt <chris.brandt@...esas.com>

commit f59de563358eb9351b7f8f0ba2d3be2ebb70b93d upstream.

When there is no status bit, it is possible for the clock enable/disable
operation to have not completed by the time the driver code resumes
execution. This is due to the fact that write operations are sometimes
queued and delayed internally. Doing a read ensures the write operations
has completed.

Fixes: b6face404f38 ("ARM: shmobile: r7s72100: add essential clock nodes to dtsi")
Signed-off-by: Chris Brandt <chris.brandt@...esas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@...der.be>
Signed-off-by: Stephen Boyd <sboyd@...eaurora.org>
[bwh: Backported to 3.16:
 - Use barrier() instead of barrier_data()
 - Adjust filename]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/clk/shmobile/clk-mstp.c | 6 ++++++
 1 file changed, 6 insertions(+)

--- a/drivers/clk/shmobile/clk-mstp.c
+++ b/drivers/clk/shmobile/clk-mstp.c
@@ -85,6 +85,12 @@ static int cpg_mstp_clock_endisable(stru
 		value |= bitmask;
 	cpg_mstp_write(group, value, group->smstpcr);
 
+	if (!group->mstpsr) {
+		/* dummy read to ensure write has completed */
+		cpg_mstp_read(group, group->smstpcr);
+		barrier();
+	}
+
 	spin_unlock_irqrestore(&group->lock, flags);
 
 	if (!enable || !group->mstpsr)