linux-kernel - Re: [PATCH 13/13 v4] drm/i915/intel_i2c: reuse GMBUS2 value read in polling loop

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Date:	Wed, 28 Mar 2012 12:44:59 +0100
From:	Chris Wilson <chris@...is-wilson.co.uk>
To:	Daniel Kurtz <djkurtz@...omium.org>
Cc:	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,
	Benson Leung <bleung@...omium.org>,
	Yufeng Shen <miletus@...omium.org>
Subject: Re: [PATCH 13/13 v4] drm/i915/intel_i2c: reuse GMBUS2 value read in polling loop

On Wed, 28 Mar 2012 19:39:17 +0800, Daniel Kurtz <djkurtz@...omium.org> wrote:
> On Wed, Mar 28, 2012 at 3:02 AM, Chris Wilson <chris@...is-wilson.co.uk> wrote:
> > Might as well shave this read as well.
> 
> Do you know why POSTING_READ() was there in the first place?
> As far as I can tell, these are used to ensure memory barriers are
> inserted between a group of writes, and subsequent reads to memory
> mapped io registers.
> However, the normal I915_READ() and I915_WRITE() macros already call
> readl() / writel(), which already have an explicit mb().
> So, can we just get rid of all of them, or am I missing something?

They can go. They were there just as paranoia to make sure the writes
were flushed before any timing delays and across loops. Once the code
settled I never took the liberty of removing them.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre
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