Re: [PATCH] drm/i915: Force clean compilation with -Werror

[Daniel Vetter <daniel@ffwll.ch>]

On Mon, Dec 14, 2015 at 02:03:33PM +0000, Chris Wilson wrote:
> Our driver compiles clean (nowadays thanks to 0day) but for me, at least,
> it would be beneficial if the compiler threw an error rather than a
> warning when it found a piece of suspect code. (I use this to
> compile-check patch series and want to break on the first compiler error
> in order to fix the patch.)
> 
> v2: Kick off a new "Debugging" submenu for i915.ko
> 
> v3: Avoid enabling -Werror for allyesconfig/allmodconfig builds, using
> COMPILE_TEST as a suitable proxy suggested by Andrew Morton. (Damien)
> Only make the option available for EXPERT to reinforce that the option
> should not be casually enabled.
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Jani Nikula <jani.nikula@intel.com>
> Cc: Damien Lespiau <damien.lespiau@intel.com>

Yeah I think we can give this another shot. Should probably reference the
last revert:

commit 908d759b210effb33d927a8cb6603a16448474e4
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Tue May 26 07:46:21 2015 +0200

    Revert "drm/i915: Force clean compilation with -Werror"

With that added:

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> ---
>  drivers/gpu/drm/i915/Kconfig       |  8 ++++++++
>  drivers/gpu/drm/i915/Kconfig.debug | 12 ++++++++++++
>  drivers/gpu/drm/i915/Makefile      |  2 ++
>  3 files changed, 22 insertions(+)
>  create mode 100644 drivers/gpu/drm/i915/Kconfig.debug
> 
> diff --git a/drivers/gpu/drm/i915/Kconfig b/drivers/gpu/drm/i915/Kconfig
> index fcd77b27514d..d493ec4c7399 100644
> --- a/drivers/gpu/drm/i915/Kconfig
> +++ b/drivers/gpu/drm/i915/Kconfig
> @@ -48,3 +48,11 @@ config DRM_I915_PRELIMINARY_HW_SUPPORT
>  	  option changes the default for that module option.
>  
>  	  If in doubt, say "N".
> +
> +menu "DRM i915 Debugging"
> +
> +depends on DRM_I915
> +
> +source drivers/gpu/drm/i915/Kconfig.debug
> +
> +endmenu
> diff --git a/drivers/gpu/drm/i915/Kconfig.debug b/drivers/gpu/drm/i915/Kconfig.debug
> new file mode 100644
> index 000000000000..1f10ee228eda
> --- /dev/null
> +++ b/drivers/gpu/drm/i915/Kconfig.debug
> @@ -0,0 +1,12 @@
> +config DRM_I915_WERROR
> +	bool "Force GCC to throw an error instead of a warning when compiling"
> +	default n
> +	# As this may inadvertently break the build, only allow the user
> +	# to shoot oneself in the foot iff they aim really hard
> +	depends on EXPERT
> +	# We use the dependency on !COMPILE_TEST to not be enabled in
> +	# allmodconfig or allyesconfig configurations
> +	depends on !COMPILE_TEST
> +	---help---
> +	  Add -Werror to the build flags for (and only for) i915.ko.
> +	  Do not enable this unless you are writing code for the i915.ko module.
> diff --git a/drivers/gpu/drm/i915/Makefile b/drivers/gpu/drm/i915/Makefile
> index 0851de07bd13..1e9895b9a546 100644
> --- a/drivers/gpu/drm/i915/Makefile
> +++ b/drivers/gpu/drm/i915/Makefile
> @@ -2,6 +2,8 @@
>  # Makefile for the drm device driver.  This driver provides support for the
>  # Direct Rendering Infrastructure (DRI) in XFree86 4.1.0 and higher.
>  
> +subdir-ccflags-$(CONFIG_DRM_I915_WERROR) := -Werror
> +
>  # Please keep these build lists sorted!
>  
>  # core driver code
> -- 
> 2.6.4
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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