linux-kernel - Re: [PATCH 08/13 v4] drm/i915/intel

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Date:	Wed, 28 Mar 2012 12:39:12 +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 08/13 v4] drm/i915/intel_i2c: handle zero-length writes

On Wed, 28 Mar 2012 19:32:27 +0800, Daniel Kurtz <djkurtz@...omium.org> wrote:
> Unfortunately there is a bug in both my original patch (it wasn't
> incrementing loop), and in your suggested cleanup (it always
> decrements len, even when it is already 0... or if the loop test
> fails).  How about the following; despite its pythonic nature, it
> always completes with len holding the number of bytes remaining.
> 
> 	val = loop = 0;
> 	while (len && loop < 4) {
> 		val |= *buf++ << (8 * loop++);
> 		len -= 1;
> 	}

I'm getting over my aversion ;-)

As we are here, have you considered doing an optimised u32 variant whilst
len >= 4, which should be reasonably common during EDID transfer. Though
I am not sure if that loop is merely in the noise compared to the rest of
the mmio.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre
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