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

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Message-ID: <1332875657_117263@CP5-2952>
Date:	Tue, 27 Mar 2012 20:14:04 +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 08/13 v4] drm/i915/intel_i2c: handle zero-length writes

On Wed, 28 Mar 2012 02:36:17 +0800, Daniel Kurtz <djkurtz@...omium.org> wrote:
> A common method of probing an i2c bus is trying to do a zero-length write.
> Handle this case by checking the length first before decrementing it.
> 
> This is actually important, since attempting a zero-length write is one
> of the ways that i2cdetect and i2c_new_probed_device detect whether
> there is device present on the bus with a given address.
> 
> Signed-off-by: Daniel Kurtz <djkurtz@...omium.org>
> ---
>  drivers/gpu/drm/i915/intel_i2c.c |    5 +++--
>  1 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_i2c.c b/drivers/gpu/drm/i915/intel_i2c.c
> index c12db72..5a94e9b 100644
> --- a/drivers/gpu/drm/i915/intel_i2c.c
> +++ b/drivers/gpu/drm/i915/intel_i2c.c
> @@ -248,9 +248,10 @@ gmbus_xfer_write(struct drm_i915_private *dev_priv, struct i2c_msg *msg,
>  	u32 val, loop;
>  
>  	val = loop = 0;
> -	do {
> +	while (len && loop < 4) {
while (len-- && loop < 4)

>  		val |= *buf++ << (8 * loop);
> -	} while (--len && ++loop < 4);
> +		len -= 1;
Otherwise this looks too pythonesque ;-)

> +	}

-- 
Chris Wilson, Intel Open Source Technology Centre
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