Re: [PATCH 14/14 v5] drm/i915/intel_i2c: remove POSTING_READ() from gmbus transfers

Chris Wilson
2012-03-28T13:05:34Z

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.
-Chris

--
Chris Wilson, Intel Open Source Technology Centre