From e1f1ae8002e4b06addc52443fcd975bbf554ae92 Mon Sep 17 00:00:00 2001 From: Geert Uytterhoeven Date: Thu, 11 Jul 2019 15:03:59 +0200 Subject: clk: renesas: cpg-mssr: Fix reset control race condition The module reset code in the Renesas CPG/MSSR driver uses read-modify-write (RMW) operations to write to a Software Reset Register (SRCRn), and simple writes to write to a Software Reset Clearing Register (SRSTCLRn), as was mandated by the R-Car Gen2 and Gen3 Hardware User's Manuals. However, this may cause a race condition when two devices are reset in parallel: if the reset for device A completes in the middle of the RMW operation for device B, device A may be reset again, causing subtle failures (e.g. i2c timeouts): thread A thread B -------- -------- val = SRCRn val |= bit A SRCRn = val delay val = SRCRn (bit A is set) SRSTCLRn = bit A (bit A in SRCRn is cleared) val |= bit B SRCRn = val (bit A and B are set) This can be reproduced on e.g. Salvator-XS using: $ while true; do i2cdump -f -y 4 0x6A b > /dev/null; done & $ while true; do i2cdump -f -y 2 0x10 b > /dev/null; done & i2c-rcar e6510000.i2c: error -110 : 40000002 i2c-rcar e66d8000.i2c: error -110 : 40000002 According to the R-Car Gen3 Hardware Manual Errata for Rev. 0.80 of Feb 28, 2018, reflected in Rev. 1.00 of the R-Car Gen3 Hardware User's Manual, writes to SRCRn do not require read-modify-write cycles. Note that the R-Car Gen2 Hardware User's Manual has not been updated yet, and still says a read-modify-write sequence is required. According to the hardware team, the reset hardware block is the same on both R-Car Gen2 and Gen3, though. Hence fix the issue by replacing the read-modify-write operations on SRCRn by simple writes. Reported-by: Yao Lihua Fixes: 6197aa65c4905532 ("clk: renesas: cpg-mssr: Add support for reset control") Signed-off-by: Geert Uytterhoeven Tested-by: Linh Phung Signed-off-by: Stephen Boyd --- drivers/clk/renesas/renesas-cpg-mssr.c | 16 ++-------------- 1 file changed, 2 insertions(+), 14 deletions(-) diff --git a/drivers/clk/renesas/renesas-cpg-mssr.c b/drivers/clk/renesas/renesas-cpg-mssr.c index 52bbb9ce3807..d4075b130674 100644 --- a/drivers/clk/renesas/renesas-cpg-mssr.c +++ b/drivers/clk/renesas/renesas-cpg-mssr.c @@ -572,17 +572,11 @@ static int cpg_mssr_reset(struct reset_controller_dev *rcdev, unsigned int reg = id / 32; unsigned int bit = id % 32; u32 bitmask = BIT(bit); - unsigned long flags; - u32 value; dev_dbg(priv->dev, "reset %u%02u\n", reg, bit); /* Reset module */ - spin_lock_irqsave(&priv->rmw_lock, flags); - value = readl(priv->base + SRCR(reg)); - value |= bitmask; - writel(value, priv->base + SRCR(reg)); - spin_unlock_irqrestore(&priv->rmw_lock, flags); + writel(bitmask, priv->base + SRCR(reg)); /* Wait for at least one cycle of the RCLK clock (@ ca. 32 kHz) */ udelay(35); @@ -599,16 +593,10 @@ static int cpg_mssr_assert(struct reset_controller_dev *rcdev, unsigned long id) unsigned int reg = id / 32; unsigned int bit = id % 32; u32 bitmask = BIT(bit); - unsigned long flags; - u32 value; dev_dbg(priv->dev, "assert %u%02u\n", reg, bit); - spin_lock_irqsave(&priv->rmw_lock, flags); - value = readl(priv->base + SRCR(reg)); - value |= bitmask; - writel(value, priv->base + SRCR(reg)); - spin_unlock_irqrestore(&priv->rmw_lock, flags); + writel(bitmask, priv->base + SRCR(reg)); return 0; } -- cgit v1.2.3-55-g7522