Re: [PATCH 3/3] drm/i915: Allow optimized platform checks

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

On Wed, 20 Sep 2017, Tvrtko Ursulin <tursulin@ursulin.net> wrote:
> From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
>
> If we store the platform as a bitmask, and convert the
> IS_PLATFORM macro to use it, we allow the compiler to
> merge the IS_PLATFORM(a) || IS_PLATFORM(b) || ... checks
> into a single conditional.
>
> Even with the added BUG_ON this saves almost 1k of text:
>
>     text           data     bss     dec     hex filename
> -1460254          60014    3656 1523924  1740d4 drivers/gpu/drm/i915/i915.ko
> +1459260          60026    3656 1522942  173cfe drivers/gpu/drm/i915/i915.ko
>
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> Cc: Jani Nikula <jani.nikula@intel.com>
> ---
>  drivers/gpu/drm/i915/i915_drv.c | 6 ++++++
>  drivers/gpu/drm/i915/i915_drv.h | 3 ++-
>  2 files changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
> index b1f96eb1be16..c3bd4b7cb19b 100644
> --- a/drivers/gpu/drm/i915/i915_drv.c
> +++ b/drivers/gpu/drm/i915/i915_drv.c
> @@ -869,6 +869,12 @@ static int i915_driver_init_early(struct drm_i915_private *dev_priv,
>  	memcpy(device_info, match_info, sizeof(*device_info));
>  	device_info->device_id = dev_priv->drm.pdev->device;
>  
> +	BUILD_BUG_ON(sizeof(device_info->platform_mask) * BITS_PER_BYTE <
> +		     (INTEL_MAX_PLATFORMS - 1));
> +	BUG_ON(device_info->platform == 0 ||
> +	       device_info->platform >= INTEL_MAX_PLATFORMS);
> +	device_info->platform_mask = BIT(device_info->platform - 1);

Please just lose the -1, pretty please?

> +
>  	BUG_ON(device_info->gen > sizeof(device_info->gen_mask) * BITS_PER_BYTE);
>  	device_info->gen_mask = BIT(device_info->gen - 1);
>  
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 950aa109f8cb..81211f23326a 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -861,6 +861,7 @@ struct intel_device_info {
>  	u8 ring_mask; /* Rings supported by the HW */
>  
>  	enum intel_platform platform;
> +	u32 platform_mask;
>  
>  	u32 display_mmio_offset;
>  
> @@ -2984,7 +2985,7 @@ intel_info(const struct drm_i915_private *dev_priv)
>  #define IS_REVID(p, since, until) \
>  	(INTEL_REVID(p) >= (since) && INTEL_REVID(p) <= (until))
>  
> -#define IS_PLATFORM(dev_priv, p) ((dev_priv)->info.platform == (p))
> +#define IS_PLATFORM(dev_priv, p) ((dev_priv)->info.platform_mask & BIT((p) - 1))

What would the result be without platform_mask and just:

#define IS_PLATFORM(dev_priv, p) (BIT((dev_priv)->info.platform) & BIT(p))


BR,
Jani.

>  
>  #define IS_I830(dev_priv)	IS_PLATFORM(dev_priv, INTEL_I830)
>  #define IS_I845G(dev_priv)	IS_PLATFORM(dev_priv, INTEL_I845G)

-- 
Jani Nikula, Intel Open Source Technology Center
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