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authorGeert Uytterhoeven <geert+renesas@glider.be>2019-07-11 15:03:59 +0200
committerStephen Boyd <sboyd@kernel.org>2019-07-22 15:04:54 -0700
commite1f1ae8002e4b06addc52443fcd975bbf554ae92 (patch)
tree67568f93bc1e1b799e49d09d6725f880fcc6e190 /drivers/clk
parentc9a67cbb5189e966c70451562b2ca4c3876ab546 (diff)
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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 <Lihua.Yao@desay-svautomotive.com> Fixes: 6197aa65c4905532 ("clk: renesas: cpg-mssr: Add support for reset control") Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be> Tested-by: Linh Phung <linh.phung.jy@renesas.com> Signed-off-by: Stephen Boyd <sboyd@kernel.org>
Diffstat (limited to 'drivers/clk')
-rw-r--r--drivers/clk/renesas/renesas-cpg-mssr.c16
1 files 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;
}