linux-kernel - Re: [PATCH 14/14 v5] drm/i915/intel_i2c: remove POSTING

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Date:	Wed, 28 Mar 2012 14:05:13 +0100
From:	Chris Wilson <chris@...is-wilson.co.uk>
To:	Daniel Kurtz <djkurtz@...omium.org>,
	Daniel Vetter <daniel@...ll.ch>,
	Keith Packard <keithp@...thp.com>,
	David Airlie <airlied@...ux.ie>,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Cc:	Benson Leung <bleung@...omium.org>,
	Yufeng Shen <miletus@...omium.org>,
	Daniel Kurtz <djkurtz@...omium.org>
Subject: Re: [PATCH 14/14 v5] drm/i915/intel_i2c: remove POSTING_READ() from gmbus transfers

On Wed, 28 Mar 2012 20:51:57 +0800, Daniel Kurtz <djkurtz@...omium.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@...omium.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
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