linux-kernel - Re: [PATCH 04/11 v3] drm/i915/intel_i2c: cleanup gmbus/gpio pin assignments

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Date:	Mon, 26 Mar 2012 17:20:11 +0200
From:	Daniel Vetter <daniel@...ll.ch>
To:	Daniel Kurtz <djkurtz@...omium.org>
Cc:	Keith Packard <keithp@...thp.com>, David Airlie <airlied@...ux.ie>,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
	Daniel Vetter <daniel@...ll.ch>,
	Chris Wilson <chris@...is-wilson.co.uk>,
	Benson Leung <bleung@...omium.org>,
	Yufeng Shen <miletus@...omium.org>
Subject: Re: [PATCH 04/11 v3] drm/i915/intel_i2c: cleanup gmbus/gpio pin
 assignments

On Mon, Mar 26, 2012 at 10:26:43PM +0800, Daniel Kurtz wrote:
> There is no GMBUS "disabled" port 0, nor "reserved" port 7.
> For the other 6 ports there is a fixed 1:1 mapping between pin pairs and
> gmbus ports, which means every real gmbus port has a gpio pin.
> 
> Given these realizations, clean up gmbus initialization.
> 
> Tested on Sandybridge (gen 6, PCH == CougarPoint) hardware.
> 
> Signed-off-by: Daniel Kurtz <djkurtz@...omium.org>
> ---
>  drivers/gpu/drm/i915/i915_drv.h  |    1 -
>  drivers/gpu/drm/i915/i915_reg.h  |    2 +-
>  drivers/gpu/drm/i915/intel_i2c.c |   63 ++++++++++++++-----------------------
>  3 files changed, 25 insertions(+), 41 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> @@ -370,16 +365,6 @@ static const struct i2c_algorithm gmbus_algorithm = {
>   */
>  int intel_setup_gmbus(struct drm_device *dev)
>  {
> -	static const char *names[GMBUS_NUM_PORTS] = {
> -		"disabled",
> -		"ssc",
> -		"vga",
> -		"panel",
> -		"dpc",
> -		"dpb",
> -		"dpd",
> -		"reserved",
> -	};
>  	struct drm_i915_private *dev_priv = dev->dev_private;
>  	int ret, i;
>  
> @@ -397,13 +382,14 @@ int intel_setup_gmbus(struct drm_device *dev)
>  
>  	for (i = 0; i < GMBUS_NUM_PORTS; i++) {
>  		struct intel_gmbus *bus = &dev_priv->gmbus[i];
> +		u32 port = i + 1; /* +1 to map gmbus index to pin pair */

On reconsideration you move around gmbus ports here, which will break
things horribly. I've wondered a bit how that could possible work and
noticed that you fix things up in the a later patch when introducing
get_adapter.

This ordering breaks bisecting is a complete no-go. If you want to do this
(I still think the refactor is nice) you need to introduce get_adapter
first, then change the meaning of the array index in this patch while
adjusting the lookup in the new get_adapter function.

Yours, Daniel
-- 
Daniel Vetter
Mail: daniel@...ll.ch
Mobile: +41 (0)79 365 57 48
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