Re: [PATCH 3/3] drm/msm: hijack firmware fb's memory

On Tue, Jul 11, 2017 at 10:17 AM, Chris Wilson [off-list ref] wrote:

Quoting Rob Clark (2017-07-11 14:38:22)

quoted

+static unsigned long hijack_firmware_fb(struct drm_device *dev)
+{
+       struct msm_drm_private *priv = dev->dev_private;
+       unsigned long size;
+       int i;
+
+       /* if we have simplefb/efifb, find it's aperture and hijack
+        * that before we kick out the firmware fb's.
+        *
+        * TODO we probably should hold registration_lock
+        */
+       for (i = 0; i < FB_MAX; i++) {
+               struct fb_info *fb = get_fb_info(i);
+
+               if (IS_ERR_OR_NULL(fb))
+                       continue;
+
+               if (!fb->apertures->count)

Does get_fb_info() not return a reference if its apertures->count=0?

yeah, you are right.. overlooked that when converting from iterating
registered_fb[] table directly without taking a reference..

quoted

+                       continue;
+
+               /* if we find efifb or simplefb, we are about to
+                * kick them out, so hijack their memory:
+                */
+               if ((strcmp(fb->fix.id, "EFI VGA") = 0) ||
+                               (strcmp(fb->fix.id, "simple") = 0)) {
+
+                       priv->vram.paddr = fb->apertures->ranges[0].base;
+                       size = fb->apertures->ranges[0].size;
+               }
+
+               put_fb_info(fb);
+
+               if (size)
+                       return size;

size is never initialised to 0. Perhaps just return the reference to the
matching fb? Hopefully sidestepping a few of the worries about it
disappearing during the probe.

I guess that would be a useful approach if I wanted a single helper
that did both this and kicking out firmware fb's..

BR,
-R