linux-kernel - Re: [PATCH 2/2] drm/i915/gvt: fix compilation

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Date:   Sat, 22 Oct 2016 13:09:41 +0800
From:   Zhenyu Wang <zhenyuw@...ux.intel.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Daniel Vetter <daniel.vetter@...el.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Zhi Wang <zhi.a.wang@...el.com>,
        Zhenyu Wang <zhenyuw@...ux.intel.com>,
        David Airlie <airlied@...ux.ie>,
        Chris Wilson <chris@...is-wilson.co.uk>,
        igvt-g-dev@...ts.01.org, intel-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] drm/i915/gvt: fix compilation

On 2016.10.21 17:25:50 +0200, Arnd Bergmann wrote:
> Two functions in the newly added gvt render code are obviously
> broken, as they reference a variable without initialization and
> don't reference another variable at all:
> 
> drivers/gpu/drm/i915/gvt/render.c: In function ???intel_gvt_load_render_mmio???:
> drivers/gpu/drm/i915/gvt/render.c:148:13: error: ???offset.reg??? may be used uninitialized in this function [-Werror=maybe-uninitialized]
> drivers/gpu/drm/i915/gvt/render.c: In function ???intel_gvt_restore_render_mmio???:
> drivers/gpu/drm/i915/gvt/render.c:185:13: error: ???offset.reg??? may be used uninitialized in this function [-Werror=maybe-uninitialized]
> 
> This is probably not a correct fix, but it gets us a clean build
> by removing the unused arrays and initializing the offset variable
> to something that potentially might be correct.
> 
> Fixes: 178657139307 ("drm/i915/gvt: vGPU context switch")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---

I think the correct fix is like

diff --git a/drivers/gpu/drm/i915/gvt/render.c b/drivers/gpu/drm/i915/gvt/render.c
index feebb65..cc23c3f 100644
--- a/drivers/gpu/drm/i915/gvt/render.c
+++ b/drivers/gpu/drm/i915/gvt/render.c
@@ -162,6 +162,7 @@ static void load_mocs(struct intel_vgpu *vgpu, int ring_id)
 	if (!IS_SKYLAKE(dev_priv))
 		return;
 
+	offset.reg = regs[ring_id];
 	for (i = 0; i < 64; i++) {
 		gen9_render_mocs[ring_id][i] = I915_READ(offset);
 		I915_WRITE(offset, vgpu_vreg(vgpu, offset));
@@ -199,6 +200,7 @@ static void restore_mocs(struct intel_vgpu *vgpu, int ring_id)
 	if (!IS_SKYLAKE(dev_priv))
 		return;
 
+	offset.reg = regs[ring_id];
 	for (i = 0; i < 64; i++) {
 		vgpu_vreg(vgpu, offset) = I915_READ(offset);
 		I915_WRITE(offset, gen9_render_mocs[ring_id][i]);

Thanks for pointing this out, it's a mistake during our code preparation for upstream.
I'll queue this up.

>  drivers/gpu/drm/i915/gvt/render.c | 25 +++----------------------
>  1 file changed, 3 insertions(+), 22 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gvt/render.c b/drivers/gpu/drm/i915/gvt/render.c
> index feebb65ba641..79e112288065 100644
> --- a/drivers/gpu/drm/i915/gvt/render.c
> +++ b/drivers/gpu/drm/i915/gvt/render.c
> @@ -147,29 +147,20 @@ static void load_mocs(struct intel_vgpu *vgpu, int ring_id)
>  {
>  	struct drm_i915_private *dev_priv = vgpu->gvt->dev_priv;
>  	i915_reg_t offset, l3_offset;
> -	u32 regs[] = {
> -		[RCS] = 0xc800,
> -		[VCS] = 0xc900,
> -		[VCS2] = 0xca00,
> -		[BCS] = 0xcc00,
> -		[VECS] = 0xcb00,
> -	};
>  	int i;
>  
> -	if (WARN_ON(ring_id >= ARRAY_SIZE(regs)))
> -		return;
> -
>  	if (!IS_SKYLAKE(dev_priv))
>  		return;
>  
>  	for (i = 0; i < 64; i++) {
> +		offset.reg = i * 4;
>  		gen9_render_mocs[ring_id][i] = I915_READ(offset);
>  		I915_WRITE(offset, vgpu_vreg(vgpu, offset));
>  		POSTING_READ(offset);
> -		offset.reg += 4;
>  	}
>  
>  	if (ring_id == RCS) {
> +		offset.reg = 64 * 4;
>  		l3_offset.reg = 0xb020;
>  		for (i = 0; i < 32; i++) {
>  			gen9_render_mocs_L3[i] = I915_READ(l3_offset);
> @@ -184,26 +175,16 @@ static void restore_mocs(struct intel_vgpu *vgpu, int ring_id)
>  {
>  	struct drm_i915_private *dev_priv = vgpu->gvt->dev_priv;
>  	i915_reg_t offset, l3_offset;
> -	u32 regs[] = {
> -		[RCS] = 0xc800,
> -		[VCS] = 0xc900,
> -		[VCS2] = 0xca00,
> -		[BCS] = 0xcc00,
> -		[VECS] = 0xcb00,
> -	};
>  	int i;
>  
> -	if (WARN_ON(ring_id >= ARRAY_SIZE(regs)))
> -		return;
> -
>  	if (!IS_SKYLAKE(dev_priv))
>  		return;
>  
>  	for (i = 0; i < 64; i++) {
> +		offset.reg = i * 4;
>  		vgpu_vreg(vgpu, offset) = I915_READ(offset);
>  		I915_WRITE(offset, gen9_render_mocs[ring_id][i]);
>  		POSTING_READ(offset);
> -		offset.reg += 4;
>  	}
>  
>  	if (ring_id == RCS) {
> -- 
> 2.9.0
> 

-- 
Open Source Technology Center, Intel ltd.

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