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

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

[Chris Wilson]

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.)

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/Makefile | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/gpu/drm/i915/Makefile b/drivers/gpu/drm/i915/Makefile
index b7ddf48e1d75..5b2a6e039500 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-y := -Werror
+
 # Please keep these build lists sorted!
 
 # core driver code
-- 
2.1.4

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

[Damien Lespiau]

On Wed, May 20, 2015 at 11:35:28AM +0100, 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.)
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

Just to repeat what was said on IRC. -Werror is usally a no-go outside
of a development environment because different compilers (which includes
different compiler versions) will have different sets of warnings, even
with the same options. It also breaks bisecting if, for instance, or
more recent toolchain produces a warning that it didn't in a previous
version and we're trying to compile an old commit.

-- 
Damien

> ---
>  drivers/gpu/drm/i915/Makefile | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/Makefile b/drivers/gpu/drm/i915/Makefile
> index b7ddf48e1d75..5b2a6e039500 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-y := -Werror
> +
>  # Please keep these build lists sorted!
>  
>  # core driver code
> -- 
> 2.1.4
> 
> _______________________________________________
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> Intel-gfx@lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/intel-gfx
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[PATCH] drm/i915: Map the execlists context regs once during pinning

[Chris Wilson]

When we pin the execlists context on queuing, it the ideal time to map
the register page that we need to update when we submit the request to
the hardware (and keep it around for future requests).

This avoids having to do an atomic kmap on every submission. On the
other hand, it does depend upon correct request construction.

v2: Rebase
v3: Rebase
v4: Rebase

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_gem.c         |  10 --
 drivers/gpu/drm/i915/i915_gem_gtt.c     |   1 +
 drivers/gpu/drm/i915/intel_lrc.c        | 216 ++++++++++++++------------------
 drivers/gpu/drm/i915/intel_lrc.h        |   2 -
 drivers/gpu/drm/i915/intel_ringbuffer.h |   1 +
 5 files changed, 95 insertions(+), 135 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 3f0b85a22eeb..b3cf3fa5716a 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2653,13 +2653,6 @@ void i915_gem_request_free(struct kref *req_ref)
 	struct intel_context *ctx = req->ctx;
 
 	if (ctx) {
-		if (i915.enable_execlists) {
-			struct intel_engine_cs *ring = req->ring;
-
-			if (ctx != ring->default_context)
-				intel_lr_context_unpin(ring, ctx);
-		}
-
 		i915_gem_context_unreference(ctx);
 	}
 
@@ -2767,9 +2760,6 @@ static void i915_gem_reset_ring_cleanup(struct drm_i915_private *dev_priv,
 				execlist_link);
 		list_del(&submit_req->execlist_link);
 
-		if (submit_req->ctx != ring->default_context)
-			intel_lr_context_unpin(ring, submit_req->ctx);
-
 		i915_gem_request_unreference(submit_req);
 	}
 
diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
index 450418b0111b..54fd17ddf0f0 100644
--- a/drivers/gpu/drm/i915/i915_gem_gtt.c
+++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
@@ -915,6 +915,7 @@ static int gen8_alloc_va_range(struct i915_address_space *vm,
 	}
 
 	free_gen8_temp_bitmaps(new_page_dirs, new_page_tables);
+	ppgtt->pd_dirty_rings = ~0;
 	return 0;
 
 err_out:
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index d6d3fc2bb77b..c8ded8b05af5 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -212,9 +212,6 @@ enum {
 };
 #define GEN8_CTX_ID_SHIFT 32
 
-static int intel_lr_context_pin(struct intel_engine_cs *ring,
-		struct intel_context *ctx);
-
 /**
  * intel_sanitize_enable_execlists() - sanitize i915.enable_execlists
  * @dev: DRM device.
@@ -330,57 +327,39 @@ static void execlists_elsp_write(struct intel_engine_cs *ring,
 	spin_unlock(&dev_priv->uncore.lock);
 }
 
-static int execlists_update_context(struct drm_i915_gem_object *ctx_obj,
-				    struct drm_i915_gem_object *ring_obj,
-				    struct i915_hw_ppgtt *ppgtt,
-				    u32 tail)
+static struct drm_i915_gem_object *
+execlists_update_context(struct intel_engine_cs *ring,
+			 struct intel_context *ctx,
+			 u32 tail)
 {
-	struct page *page;
-	uint32_t *reg_state;
-
-	page = i915_gem_object_get_page(ctx_obj, 1);
-	reg_state = kmap_atomic(page);
-
-	reg_state[CTX_RING_TAIL+1] = tail;
-	reg_state[CTX_RING_BUFFER_START+1] = i915_gem_obj_ggtt_offset_view(ring_obj, NULL);
+	struct intel_ringbuffer *ringbuf = ctx->engine[ring->id].ringbuf;
+	struct i915_hw_ppgtt *ppgtt = ctx->ppgtt;
 
 	/* True PPGTT with dynamic page allocation: update PDP registers and
 	 * point the unallocated PDPs to the scratch page
 	 */
-	if (ppgtt) {
-		ASSIGN_CTX_PDP(ppgtt, reg_state, 3);
-		ASSIGN_CTX_PDP(ppgtt, reg_state, 2);
-		ASSIGN_CTX_PDP(ppgtt, reg_state, 1);
-		ASSIGN_CTX_PDP(ppgtt, reg_state, 0);
+	if (ppgtt && ppgtt->pd_dirty_rings & intel_ring_flag(ring)) {
+		ASSIGN_CTX_PDP(ppgtt, ringbuf->regs, 3);
+		ASSIGN_CTX_PDP(ppgtt, ringbuf->regs, 2);
+		ASSIGN_CTX_PDP(ppgtt, ringbuf->regs, 1);
+		ASSIGN_CTX_PDP(ppgtt, ringbuf->regs, 0);
+		ppgtt->pd_dirty_rings &= ~intel_ring_flag(ring);
 	}
 
-	kunmap_atomic(reg_state);
-
-	return 0;
+	ringbuf->regs[CTX_RING_TAIL+1] = tail;
+	return ctx->engine[ring->id].state;
 }
 
 static void execlists_submit_contexts(struct intel_engine_cs *ring,
 				      struct intel_context *to0, u32 tail0,
 				      struct intel_context *to1, u32 tail1)
 {
-	struct drm_i915_gem_object *ctx_obj0 = to0->engine[ring->id].state;
-	struct intel_ringbuffer *ringbuf0 = to0->engine[ring->id].ringbuf;
-	struct drm_i915_gem_object *ctx_obj1 = NULL;
-	struct intel_ringbuffer *ringbuf1 = NULL;
-
-	BUG_ON(!ctx_obj0);
-
-	execlists_update_context(ctx_obj0, ringbuf0->obj, to0->ppgtt, tail0);
+	struct drm_i915_gem_object *c0, *c1;
 
-	if (to1) {
-		ringbuf1 = to1->engine[ring->id].ringbuf;
-		ctx_obj1 = to1->engine[ring->id].state;
-		BUG_ON(!ctx_obj1);
+	c0 = execlists_update_context(ring, to0, tail0);
+	c1 = to1 ? execlists_update_context(ring, to1, tail1) : NULL;
 
-		execlists_update_context(ctx_obj1, ringbuf1->obj, to1->ppgtt, tail1);
-	}
-
-	execlists_elsp_write(ring, ctx_obj0, ctx_obj1);
+	execlists_elsp_write(ring, c0, c1);
 }
 
 static void execlists_context_unqueue(struct intel_engine_cs *ring)
@@ -547,25 +526,15 @@ static int execlists_context_queue(struct intel_engine_cs *ring,
 	struct drm_i915_gem_request *cursor;
 	int num_elements = 0;
 
-	if (to != ring->default_context)
-		intel_lr_context_pin(ring, to);
+	if (WARN_ON(request == NULL))
+		return -ENODEV;
+
+	if (WARN_ON(to->engine[ring->id].pin_count == 0))
+		return -ENODEV;
+
+	i915_gem_request_reference(request);
+	WARN_ON(to != request->ctx);
 
-	if (!request) {
-		/*
-		 * If there isn't a request associated with this submission,
-		 * create one as a temporary holder.
-		 */
-		request = kzalloc(sizeof(*request), GFP_KERNEL);
-		if (request == NULL)
-			return -ENOMEM;
-		request->ring = ring;
-		request->ctx = to;
-		kref_init(&request->ref);
-		i915_gem_context_reference(request->ctx);
-	} else {
-		i915_gem_request_reference(request);
-		WARN_ON(to != request->ctx);
-	}
 	request->tail = tail;
 
 	spin_lock_irq(&ring->execlist_lock);
@@ -654,16 +623,47 @@ static int execlists_move_to_gpu(struct intel_ringbuffer *ringbuf,
 	return logical_ring_invalidate_all_caches(ringbuf, ctx);
 }
 
+static int intel_lr_context_pin(struct intel_engine_cs *ring,
+				struct intel_context *ctx)
+{
+	struct drm_i915_gem_object *ctx_obj = ctx->engine[ring->id].state;
+	struct intel_ringbuffer *ringbuf = ctx->engine[ring->id].ringbuf;
+	struct i915_vma *vma;
+
+	WARN_ON(!mutex_is_locked(&ring->dev->struct_mutex));
+	if (ctx->engine[ring->id].pin_count++)
+		return 0;
+
+	vma = i915_gem_obj_ggtt_pin(ctx_obj, GEN8_LR_CONTEXT_ALIGN, 0);
+	if (IS_ERR(vma))
+		goto reset_pin_count;
+
+	ctx->engine[ring->id].vma = vma;
+
+	vma = intel_pin_and_map_ringbuffer_obj(ring->dev, ringbuf);
+	if (IS_ERR(vma))
+		goto unpin_ctx_obj;
+
+	ringbuf->regs = kmap(i915_gem_object_get_page(ctx_obj, 1));
+	ringbuf->regs[CTX_RING_BUFFER_START+1] = vma->node.start;
+	return 0;
+
+unpin_ctx_obj:
+	i915_vma_unpin(ctx->engine[ring->id].vma);
+	ctx->engine[ring->id].vma = NULL;
+reset_pin_count:
+	ctx->engine[ring->id].pin_count = 0;
+	return PTR_ERR(vma);
+}
+
 int intel_logical_ring_alloc_request_extras(struct drm_i915_gem_request *request,
 					    struct intel_context *ctx)
 {
 	int ret;
 
-	if (ctx != request->ring->default_context) {
-		ret = intel_lr_context_pin(request->ring, ctx);
-		if (ret)
-			return ret;
-	}
+	ret = intel_lr_context_pin(request->ring, ctx);
+	if (ret)
+		return ret;
 
 	request->ringbuf = ctx->engine[request->ring->id].ringbuf;
 	request->ctx     = ctx;
@@ -913,29 +913,43 @@ int intel_execlists_submission(struct drm_device *dev, struct drm_file *file,
 	return 0;
 }
 
+static void intel_lr_context_unpin(struct intel_engine_cs *ring,
+				   struct intel_context *ctx)
+{
+	struct intel_ringbuffer *ringbuf = ctx->engine[ring->id].ringbuf;
+
+	if (--ctx->engine[ring->id].pin_count)
+		return;
+
+	kunmap(i915_gem_object_get_page(ctx->engine[ring->id].state, 1));
+	ringbuf->regs = NULL;
+
+	intel_unpin_ringbuffer_obj(ringbuf);
+
+	i915_vma_unpin(ctx->engine[ring->id].vma);
+	ctx->engine[ring->id].vma = NULL;
+}
+
 void intel_execlists_retire_requests(struct intel_engine_cs *ring)
 {
-	struct drm_i915_gem_request *req, *tmp;
-	struct list_head retired_list;
+	struct list_head list;
 
 	WARN_ON(!mutex_is_locked(&ring->dev->struct_mutex));
 	if (list_empty(&ring->execlist_retired_req_list))
 		return;
 
-	INIT_LIST_HEAD(&retired_list);
 	spin_lock_irq(&ring->execlist_lock);
-	list_replace_init(&ring->execlist_retired_req_list, &retired_list);
+	list_replace_init(&ring->execlist_retired_req_list, &list);
 	spin_unlock_irq(&ring->execlist_lock);
 
-	list_for_each_entry_safe(req, tmp, &retired_list, execlist_link) {
-		struct intel_context *ctx = req->ctx;
-		struct drm_i915_gem_object *ctx_obj =
-				ctx->engine[ring->id].state;
+	while (!list_empty(&list)) {
+		struct drm_i915_gem_request *rq;
+
+		rq = list_first_entry(&list, typeof(*rq), execlist_link);
+		list_del(&rq->execlist_link);
 
-		if (ctx_obj && (ctx != ring->default_context))
-			intel_lr_context_unpin(ring, ctx);
-		list_del(&req->execlist_link);
-		i915_gem_request_unreference(req);
+		intel_lr_context_unpin(ring, rq->ctx);
+		i915_gem_request_unreference(rq);
 	}
 }
 
@@ -978,52 +992,6 @@ int logical_ring_flush_all_caches(struct intel_ringbuffer *ringbuf,
 	return 0;
 }
 
-static int intel_lr_context_pin(struct intel_engine_cs *ring,
-		struct intel_context *ctx)
-{
-	struct drm_i915_gem_object *ctx_obj = ctx->engine[ring->id].state;
-	struct intel_ringbuffer *ringbuf = ctx->engine[ring->id].ringbuf;
-	struct i915_vma *vma;
-
-	WARN_ON(!mutex_is_locked(&ring->dev->struct_mutex));
-	if (ctx->engine[ring->id].pin_count++ == 0) {
-		vma = i915_gem_obj_ggtt_pin(ctx_obj,
-					    GEN8_LR_CONTEXT_ALIGN, 0);
-		if (IS_ERR(vma))
-			goto reset_pin_count;
-
-		ctx->engine[ring->id].vma = vma;
-
-		vma = intel_pin_and_map_ringbuffer_obj(ring->dev, ringbuf);
-		if (IS_ERR(vma))
-			goto unpin_ctx_obj;
-	}
-
-	return 0;
-
-unpin_ctx_obj:
-	i915_vma_unpin(ctx->engine[ring->id].vma);
-	ctx->engine[ring->id].pin_count = 0;
-reset_pin_count:
-	ctx->engine[ring->id].vma = NULL;
-	return PTR_ERR(vma);
-}
-
-void intel_lr_context_unpin(struct intel_engine_cs *ring,
-		struct intel_context *ctx)
-{
-	struct drm_i915_gem_object *ctx_obj = ctx->engine[ring->id].state;
-	struct intel_ringbuffer *ringbuf = ctx->engine[ring->id].ringbuf;
-
-	if (ctx_obj) {
-		WARN_ON(!mutex_is_locked(&ring->dev->struct_mutex));
-		if (--ctx->engine[ring->id].pin_count == 0) {
-			intel_unpin_ringbuffer_obj(ringbuf);
-			i915_vma_unpin(ctx->engine[ring->id].vma);
-		}
-	}
-}
-
 static int intel_logical_ring_workarounds_emit(struct intel_engine_cs *ring,
 					       struct intel_context *ctx)
 {
@@ -1780,13 +1748,15 @@ populate_lr_context(struct intel_context *ctx, struct drm_i915_gem_object *ctx_o
 	reg_state[CTX_PDP0_UDW] = GEN8_RING_PDP_UDW(ring, 0);
 	reg_state[CTX_PDP0_LDW] = GEN8_RING_PDP_LDW(ring, 0);
 
-	/* With dynamic page allocation, PDPs may not be allocated at this point,
-	 * Point the unallocated PDPs to the scratch page
+	/* With dynamic page allocation, PDPs may not be allocated at this
+	 * point. Point the unallocated PDPs to the scratch page.
 	 */
 	ASSIGN_CTX_PDP(ppgtt, reg_state, 3);
 	ASSIGN_CTX_PDP(ppgtt, reg_state, 2);
 	ASSIGN_CTX_PDP(ppgtt, reg_state, 1);
 	ASSIGN_CTX_PDP(ppgtt, reg_state, 0);
+	ctx->ppgtt->pd_dirty_rings &= ~intel_ring_flag(ring);
+
 	if (ring->id == RCS) {
 		reg_state[CTX_LRI_HEADER_2] = MI_LOAD_REGISTER_IMM(1);
 		reg_state[CTX_R_PWR_CLK_STATE] = GEN8_R_PWR_CLK_STATE;
@@ -2003,7 +1973,7 @@ error_unpin_ctx:
 }
 
 void intel_lr_context_reset(struct drm_device *dev,
-			struct intel_context *ctx)
+			    struct intel_context *ctx)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	struct intel_engine_cs *ring;
diff --git a/drivers/gpu/drm/i915/intel_lrc.h b/drivers/gpu/drm/i915/intel_lrc.h
index 49828f1f5708..9c91bf915a64 100644
--- a/drivers/gpu/drm/i915/intel_lrc.h
+++ b/drivers/gpu/drm/i915/intel_lrc.h
@@ -70,8 +70,6 @@ static inline void intel_logical_ring_emit(struct intel_ringbuffer *ringbuf,
 void intel_lr_context_free(struct intel_context *ctx);
 int intel_lr_context_deferred_create(struct intel_context *ctx,
 				     struct intel_engine_cs *ring);
-void intel_lr_context_unpin(struct intel_engine_cs *ring,
-		struct intel_context *ctx);
 void intel_lr_context_reset(struct drm_device *dev,
 			struct intel_context *ctx);
 
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
index ce2ae5f7dc00..398afe256081 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.h
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
@@ -96,6 +96,7 @@ struct intel_ring_hangcheck {
 struct intel_ringbuffer {
 	struct drm_i915_gem_object *obj;
 	void __iomem *virtual_start;
+	uint32_t *regs;
 
 	struct intel_engine_cs *ring;
 	struct i915_vma *vma;
-- 
2.1.4

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Re: [PATCH] drm/i915: Map the execlists context regs once during pinning

[Chris Wilson]

On Wed, May 20, 2015 at 02:12:37PM +0100, Chris Wilson wrote:
> When we pin the execlists context on queuing, it the ideal time to map
> the register page that we need to update when we submit the request to
> the hardware (and keep it around for future requests).
> 
> This avoids having to do an atomic kmap on every submission. On the
> other hand, it does depend upon correct request construction.

Obviously this is the wrong patch for this thread ;-)
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre
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[PATCH] drm/i915: Force clean compilation with -Werror

[Chris Wilson]

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

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/Kconfig       | 8 ++++++++
 drivers/gpu/drm/i915/Kconfig.debug | 5 +++++
 drivers/gpu/drm/i915/Makefile      | 2 ++
 3 files changed, 15 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 74acca9bcd9d..76c425ca2a2c 100644
--- a/drivers/gpu/drm/i915/Kconfig
+++ b/drivers/gpu/drm/i915/Kconfig
@@ -71,3 +71,11 @@ config DRM_I915_PRELIMINARY_HW_SUPPORT
 	  option changes the default for that module option.
 
 	  If in doubt, say "N".
+
+menu "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..070a03527bc5
--- /dev/null
+++ b/drivers/gpu/drm/i915/Kconfig.debug
@@ -0,0 +1,5 @@
+config DRM_I915_WERROR
+	bool "Force GCC to throw an error instead of a warning when compiling"
+	default n
+	---help---
+	  Add -Werror to the build flags for (and only for) i915.ko
diff --git a/drivers/gpu/drm/i915/Makefile b/drivers/gpu/drm/i915/Makefile
index b7ddf48e1d75..93d99b744531 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
-- 
2.1.4

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

[Damien Lespiau]

On Wed, May 20, 2015 at 02:12:47PM +0100, 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
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

I believe we could shove a few interesting things into that menu, sounds
like a potentially useful thing to me:

Acked-by: Damien Lespiau <damien.lespiau@intel.com>

-- 
Damien

> ---
>  drivers/gpu/drm/i915/Kconfig       | 8 ++++++++
>  drivers/gpu/drm/i915/Kconfig.debug | 5 +++++
>  drivers/gpu/drm/i915/Makefile      | 2 ++
>  3 files changed, 15 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 74acca9bcd9d..76c425ca2a2c 100644
> --- a/drivers/gpu/drm/i915/Kconfig
> +++ b/drivers/gpu/drm/i915/Kconfig
> @@ -71,3 +71,11 @@ config DRM_I915_PRELIMINARY_HW_SUPPORT
>  	  option changes the default for that module option.
>  
>  	  If in doubt, say "N".
> +
> +menu "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..070a03527bc5
> --- /dev/null
> +++ b/drivers/gpu/drm/i915/Kconfig.debug
> @@ -0,0 +1,5 @@
> +config DRM_I915_WERROR
> +	bool "Force GCC to throw an error instead of a warning when compiling"
> +	default n
> +	---help---
> +	  Add -Werror to the build flags for (and only for) i915.ko
> diff --git a/drivers/gpu/drm/i915/Makefile b/drivers/gpu/drm/i915/Makefile
> index b7ddf48e1d75..93d99b744531 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
> -- 
> 2.1.4
> 
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/intel-gfx
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Re: [PATCH] drm/i915: Force clean compilation with -Werror

[Chris Wilson]

On Wed, May 20, 2015 at 02:55:35PM +0100, Damien Lespiau wrote:
> On Wed, May 20, 2015 at 02:12:47PM +0100, 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
> > 
> > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> 
> I believe we could shove a few interesting things into that menu, sounds
> like a potentially useful thing to me:
> 
> Acked-by: Damien Lespiau <damien.lespiau@intel.com>
> 
> -- 
> Damien
> 
> > ---
> >  drivers/gpu/drm/i915/Kconfig       | 8 ++++++++
> >  drivers/gpu/drm/i915/Kconfig.debug | 5 +++++
> >  drivers/gpu/drm/i915/Makefile      | 2 ++
> >  3 files changed, 15 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 74acca9bcd9d..76c425ca2a2c 100644
> > --- a/drivers/gpu/drm/i915/Kconfig
> > +++ b/drivers/gpu/drm/i915/Kconfig
> > @@ -71,3 +71,11 @@ config DRM_I915_PRELIMINARY_HW_SUPPORT
> >  	  option changes the default for that module option.
> >  
> >  	  If in doubt, say "N".
> > +
> > +menu "Debugging"

This has to be something more like "DRM I915_Debugging" as it is
presented to the user without context in make oldconfig and appears
verbatim in .config.
-Chris

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

[Jani Nikula]

On Wed, 20 May 2015, Chris Wilson <chris@chris-wilson.co.uk> 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
>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/Kconfig       | 8 ++++++++
>  drivers/gpu/drm/i915/Kconfig.debug | 5 +++++
>  drivers/gpu/drm/i915/Makefile      | 2 ++
>  3 files changed, 15 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 74acca9bcd9d..76c425ca2a2c 100644
> --- a/drivers/gpu/drm/i915/Kconfig
> +++ b/drivers/gpu/drm/i915/Kconfig
> @@ -71,3 +71,11 @@ config DRM_I915_PRELIMINARY_HW_SUPPORT
>  	  option changes the default for that module option.
>  
>  	  If in doubt, say "N".
> +
> +menu "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..070a03527bc5
> --- /dev/null
> +++ b/drivers/gpu/drm/i915/Kconfig.debug
> @@ -0,0 +1,5 @@
> +config DRM_I915_WERROR
> +	bool "Force GCC to throw an error instead of a warning when compiling"
> +	default n
> +	---help---
> +	  Add -Werror to the build flags for (and only for) i915.ko
> diff --git a/drivers/gpu/drm/i915/Makefile b/drivers/gpu/drm/i915/Makefile
> index b7ddf48e1d75..93d99b744531 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

arch/powerpc seems to have a similar thing.

Acked-by: Jani Nikula <jani.nikula@intel.com>

---

I see that we're clean also with

  -Wall -Wextra -Wno-unused-parameter -Wno-missing-field-initializers -Wno-override-init

so could have those with e.g. subdir-ccflags-$(CONFIG_DRM_I915_WEXTRA).

I might argue we could and should get rid of
-Wno-missing-field-initializers -Wno-override-init too...

BR,
Jani.




> +
>  # Please keep these build lists sorted!
>  
>  # core driver code
> -- 
> 2.1.4
>
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/intel-gfx

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

[Daniel Vetter]

On Thu, May 21, 2015 at 10:22:17AM +0300, Jani Nikula wrote:
> On Wed, 20 May 2015, Chris Wilson <chris@chris-wilson.co.uk> 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
> >
> > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> > ---
> >  drivers/gpu/drm/i915/Kconfig       | 8 ++++++++
> >  drivers/gpu/drm/i915/Kconfig.debug | 5 +++++
> >  drivers/gpu/drm/i915/Makefile      | 2 ++
> >  3 files changed, 15 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 74acca9bcd9d..76c425ca2a2c 100644
> > --- a/drivers/gpu/drm/i915/Kconfig
> > +++ b/drivers/gpu/drm/i915/Kconfig
> > @@ -71,3 +71,11 @@ config DRM_I915_PRELIMINARY_HW_SUPPORT
> >  	  option changes the default for that module option.
> >  
> >  	  If in doubt, say "N".
> > +
> > +menu "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..070a03527bc5
> > --- /dev/null
> > +++ b/drivers/gpu/drm/i915/Kconfig.debug
> > @@ -0,0 +1,5 @@
> > +config DRM_I915_WERROR
> > +	bool "Force GCC to throw an error instead of a warning when compiling"
> > +	default n
> > +	---help---
> > +	  Add -Werror to the build flags for (and only for) i915.ko
> > diff --git a/drivers/gpu/drm/i915/Makefile b/drivers/gpu/drm/i915/Makefile
> > index b7ddf48e1d75..93d99b744531 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
> 
> arch/powerpc seems to have a similar thing.
> 
> Acked-by: Jani Nikula <jani.nikula@intel.com>

Ok let's give this a shot and see what happens. Queued for -next, thanks
for the patch.
-Daniel
> 
> ---
> 
> I see that we're clean also with
> 
>   -Wall -Wextra -Wno-unused-parameter -Wno-missing-field-initializers -Wno-override-init
> 
> so could have those with e.g. subdir-ccflags-$(CONFIG_DRM_I915_WEXTRA).
> 
> I might argue we could and should get rid of
> -Wno-missing-field-initializers -Wno-override-init too...
> 
> BR,
> Jani.
> 
> 
> 
> 
> > +
> >  # Please keep these build lists sorted!
> >  
> >  # core driver code
> > -- 
> > 2.1.4
> >
> > _______________________________________________
> > Intel-gfx mailing list
> > Intel-gfx@lists.freedesktop.org
> > http://lists.freedesktop.org/mailman/listinfo/intel-gfx
> 
> -- 
> Jani Nikula, Intel Open Source Technology Center
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/intel-gfx

-- 
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Software Engineer, Intel Corporation
http://blog.ffwll.ch
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Re: [PATCH] drm/i915: Force clean compilation with -Werror

[shuang.he]

Tested-By: Intel Graphics QA PRTS (Patch Regression Test System Contact: shuang.he@intel.com)
Task id: 6440
-------------------------------------Summary-------------------------------------
Platform          Delta          drm-intel-nightly          Series Applied
PNV                                  276/276              276/276
ILK                                  302/302              302/302
SNB                 -1              315/315              314/315
IVB                                  343/343              343/343
BYT                                  287/287              287/287
BDW                                  321/321              321/321
-------------------------------------Detailed-------------------------------------
Platform  Test                                drm-intel-nightly          Series Applied
*SNB  igt@pm_rpm@dpms-mode-unset-non-lpsp      PASS(1)      DMESG_WARN(1)
(dmesg patch applied)WARNING:at_drivers/gpu/drm/i915/intel_uncore.c:#assert_device_not_suspended[i915]()@WARNING:.* at .* assert_device_not_suspended+0x
Note: You need to pay more attention to line start with '*'
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Re: [PATCH] drm/i915: Force clean compilation with -Werror

[shuang.he]

Tested-By: Intel Graphics QA PRTS (Patch Regression Test System Contact: shuang.he@intel.com)
Task id: 6438
-------------------------------------Summary-------------------------------------
Platform          Delta          drm-intel-nightly          Series Applied
PNV                                  276/276              276/276
ILK                                  302/302              302/302
SNB                 -1              315/315              314/315
IVB                                  343/343              343/343
BYT                                  287/287              287/287
BDW                                  321/321              321/321
-------------------------------------Detailed-------------------------------------
Platform  Test                                drm-intel-nightly          Series Applied
*SNB  igt@pm_rpm@dpms-mode-unset-non-lpsp      PASS(1)      DMESG_WARN(1)
(dmesg patch applied)WARNING:at_drivers/gpu/drm/i915/intel_uncore.c:#assert_device_not_suspended[i915]()@WARNING:.* at .* assert_device_not_suspended+0x
Note: You need to pay more attention to line start with '*'
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[PATCH] drm/i915: Force clean compilation with -Werror

[Chris Wilson]

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

[Daniel Vetter]

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
> 
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/intel-gfx

-- 
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Software Engineer, Intel Corporation
http://blog.ffwll.ch
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[PATCH] drm/i915: Force clean compilation with -Werror

[Chris Wilson]

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

At this point, we applied it to the kernel and promptly kicked it out
again as it broke buildbots (due to a compiler warning on 32bits):

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"

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

[Chris Wilson]

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

At this point, we applied it to the kernel and promptly kicked it out
again as it broke buildbots (due to a compiler warning on 32bits):

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"

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>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
---

This is a test! I'm seeing whether I can route git send-email through gmail.
Thanks for your patience.
-Chris

---
 drivers/gpu/drm/i915/Kconfig       |  6 ++++++
 drivers/gpu/drm/i915/Kconfig.debug | 12 ++++++++++++
 drivers/gpu/drm/i915/Makefile      |  2 ++
 3 files changed, 20 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 b979295aab82..33e8563c2f99 100644
--- a/drivers/gpu/drm/i915/Kconfig
+++ b/drivers/gpu/drm/i915/Kconfig
@@ -59,3 +59,9 @@ config DRM_I915_USERPTR
 	  selected to enabled full userptr support.
 
 	  If in doubt, say "Y".
+
+menu "drm/i915 Debugging"
+depends on DRM_I915
+depends on EXPERT
+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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