Re: Buiild error in i915/xe (was: [PATCH next 4/7] minmax.h: Use BUILD_BUG_ON_MSG() for the lo < hi test in clamp())

[David Laight <david.laight.linux@gmail.com>]

On Sat, 18 Jan 2025 09:49:21 -0800
Guenter Roeck <linux@roeck-us.net> wrote:

> On Sat, Jan 18, 2025 at 05:09:59PM +0000, David Laight wrote:
> > On Sat, 18 Jan 2025 08:13:06 -0800
> > Guenter Roeck <linux@roeck-us.net> wrote:
> >   
> > > Hi,
> > > 
> > > On Mon, Nov 18, 2024 at 07:13:31PM +0000, David Laight wrote:  
> > > > Use BUILD_BUG_ON_MSG(statically_true(ulo > uhi), ...) for the sanity
> > > > check of the bounds in clamp().
> > > > Gives better error coverage and one less expansion of the arguments.
> > > > 
> > > > Signed-off-by: David Laight <david.laight@aculab.com>    
> > > 
> > > This patch triggers a build error when trying to build parisc:allmodconfig.
> > > See error message and bisect log below.
> > > 
> > > I don't think there is anything wrong with the patch. The underlying
> > > problem seems to be that parisc:allmodconfig enables CONFIG_DRM_XE which
> > > tries to build the affected file even though CONFIG_DRM_I915 is not
> > > enabled/supported on parisc.  
> > 
> > This has appeared before.
> > Any idea which inlined copy of scale() is causing the problem.
> > On the face of it they all look ok.
> > 
> > If you can reproduce it maybe try commenting out some of the calls.
> >   
> 
> See diff below. All three changes are needed.
> No idea why the compiler would know that the values are invalid.

Maybe it isn't even an inlining issue.
Perhaps that compiler just doesn't like the function ?
What happens without the 'static' (and an extra prototype)?

	David

> 
> Guenter
> 
> ---
> diff --git a/drivers/gpu/drm/i915/display/intel_backlight.c b/drivers/gpu/drm/i915/display/intel_backlight.c
> index fc1e517e074a..3b2c8bdfcf8d 100644
> --- a/drivers/gpu/drm/i915/display/intel_backlight.c
> +++ b/drivers/gpu/drm/i915/display/intel_backlight.c
> @@ -76,10 +76,14 @@ static u32 clamp_user_to_hw(struct intel_connector *connector,
>  static u32 scale_hw_to_user(struct intel_connector *connector,
>  			    u32 hw_level, u32 user_max)
>  {
> +#if 0
>  	struct intel_panel *panel = &connector->panel;
>  
>  	return scale(hw_level, panel->backlight.min, panel->backlight.max,
>  		     0, user_max);
> +#else
> +	return 0;
> +#endif
>  }
>  
>  u32 intel_backlight_invert_pwm_level(struct intel_connector *connector, u32 val)
> @@ -119,8 +123,10 @@ u32 intel_backlight_level_to_pwm(struct intel_connector *connector, u32 val)
>  	drm_WARN_ON_ONCE(&i915->drm,
>  			 panel->backlight.max == 0 || panel->backlight.pwm_level_max == 0);
>  
> +#if 0
>  	val = scale(val, panel->backlight.min, panel->backlight.max,
>  		    panel->backlight.pwm_level_min, panel->backlight.pwm_level_max);
> +#endif
>  
>  	return intel_backlight_invert_pwm_level(connector, val);
>  }
> @@ -138,8 +144,12 @@ u32 intel_backlight_level_from_pwm(struct intel_connector *connector, u32 val)
>  	     intel_has_quirk(display, QUIRK_INVERT_BRIGHTNESS)))
>  		val = panel->backlight.pwm_level_max - (val - panel->backlight.pwm_level_min);
>  
> +#if 0
>  	return scale(val, panel->backlight.pwm_level_min, panel->backlight.pwm_level_max,
>  		     panel->backlight.min, panel->backlight.max);
> +#else
> +	return 0;
> +#endif
>  }
>  
>  static u32 lpt_get_backlight(struct intel_connector *connector, enum pipe unused)