Le 02/11/2016 à 19:14, Maxime Ripard a écrit :
> Hi,
>
> On Sun, Oct 30, 2016 at 12:53:02PM +0100, Christophe JAILLET wrote:
>> BTW, memory allocation in 'sun4i_layers_init()' looks spurious, especially
>> the use of 'layer' in the for loop.
>> Just my 2 cents.
> What do you mean by it's spurious?
Hi Maxime,
what I mean is:
> struct sun4i_layer **sun4i_layers_init(struct drm_device *drm)
> {
> struct sun4i_drv *drv = drm->dev_private;
> struct sun4i_layer **layers;
> int i;
>
> layers = devm_kcalloc(drm->dev, ARRAY_SIZE(sun4i_backend_planes),
> sizeof(**layers), GFP_KERNEL);
Here, we allocate some memory for ARRAY_SIZE(sun4i_backend_planes) (i.e.
2) 'struct sun4i_layer'.
We do not allocate some space for some pointers but for some structure.
Also, these structures are zeroed and seem to never be initialized by
anything else.
> if (!layers)
> return ERR_PTR(-ENOMEM);
>
> /*
> * The hardware is a bit unusual here.
> *
> * Even though it supports 4 layers, it does the composition
> * in two separate steps.
> *
> * The first one is assigning a layer to one of its two
> * pipes. If more that 1 layer is assigned to the same pipe,
> * and if pixels overlaps, the pipe will take the pixel from
> * the layer with the highest priority.
> *
> * The second step is the actual alpha blending, that takes
> * the two pipes as input, and uses the eventual alpha
> * component to do the transparency between the two.
> *
> * This two steps scenario makes us unable to guarantee a
> * robust alpha blending between the 4 layers in all
> * situations. So we just expose two layers, one per pipe. On
> * SoCs that support it, sprites could fill the need for more
> * layers.
> */
The comment make me think that this driver (and this function) only
handles 2 layers ("So we just expose two layers"), which is consistent
with ARRAY_SIZE(sun4i_backend_planes) (i.e. 2)
So I would expect that only 2 'struct sun4i_layer' to be allcoated
> for (i = 0; i < ARRAY_SIZE(sun4i_backend_planes); i++) {
> const struct sun4i_plane_desc *plane = &sun4i_backend_planes[i];
> struct sun4i_layer *layer = layers[i];
Here, we take the address of one of the 2 structure allocated above.
This is overridden, just the line after.
>
> layer = sun4i_layer_init_one(drm, plane);
'sun4i_layer_init_one()' looks() like:
struct sun4i_layer *layer;
layer = devm_kzalloc(drm->dev, sizeof(*layer), GFP_KERNEL);
...
return layer;
So we once more allocate some 'struct sun4i_layer'
BUT, the corresponding address is stored into the 'layer' variable, and
finally seems to get lost and no reference is kept of this. (i.e.
'layers' (with an s) is left unchanged)
> if (IS_ERR(layer)) {
> dev_err(drm->dev, "Couldn't initialize %s plane\n",
> i ? "overlay" : "primary");
> return ERR_CAST(layer);
> };
>
> DRM_DEBUG_DRIVER("Assigning %s plane to pipe %d\n",
> i ? "overlay" : "primary", plane->pipe);
> regmap_update_bits(drv->backend->regs,
SUN4I_BACKEND_ATTCTL_REG0(i),
> SUN4I_BACKEND_ATTCTL_REG0_LAY_PIPESEL_MASK,
> SUN4I_BACKEND_ATTCTL_REG0_LAY_PIPESEL(plane->pipe));
>
> layer->id = i;
> };
>
> return layers;
> }
So, 4 'struct sun4i_layer' have been allocated. 2 in
'sun4i_layers_init()' and 2 in 'sun4i_layer_init_one()' (once at a time,
but called twice)
What looks spurious to me is either:
- 'struct sun4i_layer *layer = layers[i];' which should just be
'struct sun4i_layer *layer;'
or
- 'layers' (with an s) should be an array of pointers and the
addresses returned by 'sun4i_layer_init_one()' should be saved there.
I don't know at all this driver, so I'm maybe completely wrong.
What I would have expected would be something like: (un-tested, just to
give an idea)
==============8<================================================
@@ -133,9 +133,9 @@ struct sun4i_layer **sun4i_layers_init(struct
drm_device *drm)
struct sun4i_layer **layers;
int i;
layers = devm_kcalloc(drm->dev, ARRAY_SIZE(sun4i_backend_planes),
- sizeof(**layers), GFP_KERNEL);
+ sizeof(*layers), GFP_KERNEL);
if (!layers)
return ERR_PTR(-ENOMEM);
/*
@@ -160,16 +160,17 @@ struct sun4i_layer **sun4i_layers_init(struct
drm_device *drm)
* layers.
*/
for (i = 0; i < ARRAY_SIZE(sun4i_backend_planes); i++) {
const struct sun4i_plane_desc *plane = &sun4i_backend_planes[i];
- struct sun4i_layer *layer = layers[i];
+ struct sun4i_layer *layer;
layer = sun4i_layer_init_one(drm, plane);
if (IS_ERR(layer)) {
dev_err(drm->dev, "Couldn't initialize %s plane\n",
i ? "overlay" : "primary");
return ERR_CAST(layer);
};
+ layers[i] = layer;
DRM_DEBUG_DRIVER("Assigning %s plane to pipe %d\n",
i ? "overlay" : "primary", plane->pipe);
regmap_update_bits(drv->backend->regs,
SUN4I_BACKEND_ATTCTL_REG0(i),
Best regards,
CJ
