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    Subject[PATCH v3 5/5] reset: simple: read back to make sure changes are applied
    Date
    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@pengutronix.de>
    ---
    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
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