Le mardi 28 février 2023 à 14:36 -0500, Nicolas Dufresne a écrit : > Le mardi 28 février 2023 à 17:52 +0100, Hans Verkuil a écrit : > > While working on the vb2 conversion of the saa7146 driver I dug a bit deeper into > > the video capture overlay support of that driver. > > > > For more info of that feature see: > > > > https://linuxtv.org/downloads/v4l-dvb-apis-new/userspace-api/v4l/dev-overlay.html > > > > Specifically, video overlay support relies on userspace passing the address of > > the framebuffer to the driver with VIDIOC_S_FBUF. The PCI driver can then DMA > > the captured frame straight into the framebuffer. This was useful 20 years ago, > > but today not so much. > > > > Typically userspace would get the address from the /dev/fbX device using the > > FBIOGET_FSCREENINFO ioctl. > > > > But drm_fb_helper.c sets the smem_start field explicitly to 0 unless: > > > > 1) CONFIG_DRM_FBDEV_LEAK_PHYS_SMEM is set, and > > 2) CONFIG_EXPERT is set, and > > 3) set the drm_kms_helper module parameter drm_leak_fbdev_smem to 1. > > > > Actually, even with all that set, I *still* get a 0 value. I probably > > missed something. > > > > In any case, I think destructive overlay support is effectively dead and it > > should be removed from the v4l2 drivers. > > > > This would affect saa7146, bttv, saa7134 and vivid. > > > > Output overlay support is still around (ivtv, omap_vout). There is also a > > single driver with a non-destructive capture overlay: > > drivers/staging/vc04_services/bcm2835-camera/bcm2835-camera.c > > > > No idea what that's doing exactly in the bcm2835 driver. > > On the Pi, the firmware implements arbitrary number of graphic layers. It will > start rendering the camera on a layer on top. It is non-destructive, but on > newer code base, using libcamera, they replaced that with a QT popup window. So > maybe they also consider this as their legacy. Maybe it will make more sense if I mention that the firmware can encode the stream and pass it as H.264, while displaying the overlay. regards, Nicolas > > Note this is CAPTURE overlay, they don't do OUTPUT overlay in any drivers there. > > > > > Removing support for this has some nice related benefits: the overlay > > window supports clipping (either a list of rectangles or a bitmap), and > > that would also disappear. That makes the compat32 code quite a bit easier. > > A fair amount of code is dedicated to that. > > > > So, I propose to drop destructive overlay support from saa7146, bttv and > > saa7134 and vivid for the 6.4 kernel. In addition, support for > > V4L2_FBUF_CAP_LIST_CLIPPING and V4L2_FBUF_CAP_BITMAP_CLIPPING is also > > dropped. This only affects the vivid driver which is the only driver that > > supports this for output overlays. > > > > Any objections? > > > > Regards, > > > > Hans >
