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    SubjectRe: [PATCH 14/14 v5] drm/i915/intel_i2c: remove POSTING_READ() from gmbus transfers
    On Wed, Mar 28, 2012 at 9:05 PM, Chris Wilson <chris@chris-wilson.co.uk> wrote:
    > On Wed, 28 Mar 2012 20:51:57 +0800, Daniel Kurtz <djkurtz@chromium.org> wrote:
    >> The POSTING_READ() calls were originally added to make sure the writes
    >> were flushed before any timing delays and across loops.
    >> However, the normal I915_READ() and I915_WRITE() macros already call
    >> readl() / writel(), which already have an explicit mb().
    >>
    >> Now that the code has settled a bit, let's remove them.
    >>
    >> Signed-off-by: Daniel Kurtz <djkurtz@chromium.org>
    >> ---
    >>  drivers/gpu/drm/i915/intel_i2c.c |    5 -----
    >>  1 files changed, 0 insertions(+), 5 deletions(-)
    >>
    >> diff --git a/drivers/gpu/drm/i915/intel_i2c.c b/drivers/gpu/drm/i915/intel_i2c.c
    >> index 2865313..be2852e 100644
    >> --- a/drivers/gpu/drm/i915/intel_i2c.c
    >> +++ b/drivers/gpu/drm/i915/intel_i2c.c
    >> @@ -131,7 +131,6 @@ static void set_clock(void *data, int state_high)
    >>                       GPIO_CLOCK_VAL_MASK;
    >>
    >>       I915_WRITE_NOTRACE(bus->gpio_reg, reserved | clock_bits);
    >> -     POSTING_READ(bus->gpio_reg);
    > We do need the write flush here (and set_data) as the next action is a
    > udelay loop which is not per-se a mb.

    Now I am confused. I915_WRITE_NOTRACE() calls writel(), which has an
    explicit mb(); Why do you need another mb?

    > -Chris
    >
    > --
    > Chris Wilson, Intel Open Source Technology Centre
    --
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