Re: [PATCH 08/13 v4] drm/i915/intel_i2c: handle zero-length writes

[Chris Wilson]

On Wed, 28 Mar 2012 02:36:17 +0800, Daniel Kurtz <djkurtz@xxxxxxxxxxxx> 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@xxxxxxxxxxxx>
> ---
>  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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