[PATCH v3 5/5] reset: simple: read back to make sure changes are applied

From: Philipp Zabel
Date: Wed Aug 16 2017 - 05:48:10 EST


Read back the register after setting or clearing a reset bit to make
sure that the changes are applied to the reset controller hardware.
Theoretically, this avoids the write to stay stuck in a store buffer
during the delay of an assert-delay-deassert sequence, and makes sure
that the reset really is asserted for the specified duration.

Signed-off-by: Philipp Zabel <p.zabel@xxxxxxxxxxxxxx>
---
drivers/reset/reset-simple.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/reset/reset-simple.c b/drivers/reset/reset-simple.c
index 13e7d5559acc9..d98a7e7d802d1 100644
--- a/drivers/reset/reset-simple.c
+++ b/drivers/reset/reset-simple.c
@@ -39,17 +39,20 @@ static int reset_simple_set(struct reset_controller_dev *rcdev,
int reg_width = sizeof(u32);
int bank = id / (reg_width * BITS_PER_BYTE);
int offset = id % (reg_width * BITS_PER_BYTE);
+ void __iomem *addr = data->membase + (bank * reg_width);
unsigned long flags;
u32 reg;

spin_lock_irqsave(&data->lock, flags);

- reg = readl(data->membase + (bank * reg_width));
+ reg = readl(addr);
if (assert ^ data->active_low)
reg |= BIT(offset);
else
reg &= ~BIT(offset);
- writel(reg, data->membase + (bank * reg_width));
+ writel(reg, addr);
+ /* Read back to make sure the write doesn't linger in a store buffer */
+ readl(addr);

spin_unlock_irqrestore(&data->lock, flags);

--
2.11.0