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

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 20/09/2017 10:27, Tvrtko Ursulin 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

Forgot to say, this patch could also be called "32 platforms should be 
enough for everyone". :) Once we go over it (at 27 at the moment) we'd 
have to bump the platform_mask to u64 and the overall effect might be 
negative then. I better check that..

Regards,

Tvrtko

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