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. 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
