Re: [PATCH 2/2] drm/i915: Agnostic INTEL_INFO

[Jani Nikula <jani.nikula@linux.intel.com>]

On Sat, 09 Aug 2014, Chris Wilson <chris@chris-wilson.co.uk> wrote:
> Adapt the macro so that we can pass either the struct drm_device or the
> struct drm_i915_private pointers and get the answer we want. Over time,
> my plan is to convert all users over to using drm_i915_private and so
> trimming down the pointer dance. Having spent a few hours chasing that
> goal and achieved over 8k of object code saving, it appears to be a
> worthwhile target. This interim macro allows us to slowly convert over.
>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/i915_dma.c | 3 +++
>  drivers/gpu/drm/i915/i915_drv.h | 3 ++-
>  2 files changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_dma.c b/drivers/gpu/drm/i915/i915_dma.c
> index 39988940d468..49149406fcd8 100644
> --- a/drivers/gpu/drm/i915/i915_dma.c
> +++ b/drivers/gpu/drm/i915/i915_dma.c
> @@ -1585,6 +1585,9 @@ int i915_driver_load(struct drm_device *dev, unsigned long flags)
>  	if (!drm_core_check_feature(dev, DRIVER_MODESET) && !dev->agp)
>  		return -EINVAL;
>  
> +	/* For the ugly agnostic INTEL_INFO macro */
> +	BUILD_BUG_ON(sizeof(*dev_priv) == sizeof(*dev));
> +
>  	dev_priv = kzalloc(sizeof(*dev_priv), GFP_KERNEL);
>  	if (dev_priv == NULL)
>  		return -ENOMEM;
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 0aef763ffa75..e66465430bdc 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -2063,7 +2063,8 @@ struct drm_i915_cmd_table {
>  	int count;
>  };
>  
> -#define INTEL_INFO(p) 	(&to_i915(p)->info)
> +#define __I915__(p)	((sizeof(*(p)) == sizeof(struct drm_i915_private)) ? (struct drm_i915_private *)(p) : to_i915((struct drm_device *)p))

The explicit casts make me uncomfortable. Indeed, aren't they completely
unnecessary? If the sizeof matches, p is expected to be struct
drm_i915_private *, and if not, it's expected to be struct drm_device *,
right?

#define __I915__(p)	((sizeof(*(p)) == sizeof(struct drm_i915_private)) ? (p) : to_i915(p))

Otherwise you won't even get a compiler warning if you pass a random
pointer to this macro.

BR,
Jani.



> +#define INTEL_INFO(p) 	(&__I915__(p)->info)
>  #define INTEL_DEVID(p)	(INTEL_INFO(p)->device_id)
>  
>  #define IS_I830(dev)		(INTEL_DEVID(dev) == 0x3577)
> -- 
> 2.1.0.rc1
>
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-- 
Jani Nikula, Intel Open Source Technology Center