From: Geert Uytterhoeven geert+renesas@glider.be
[ Upstream commit e1f1ae8002e4b06addc52443fcd975bbf554ae92 ]
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 Signed-off-by: Sasha Levin sashal@kernel.org --- 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 0201809bbd377..9dfa28d6fd9f9 100644 --- a/drivers/clk/renesas/renesas-cpg-mssr.c +++ b/drivers/clk/renesas/renesas-cpg-mssr.c @@ -576,17 +576,11 @@ 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); @@ -603,16 +597,10 @@ 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; }