Am Freitag, den 21.10.2016, 16:49 +0800 schrieb Ying Liu: > On Fri, Oct 21, 2016 at 4:18 PM, Philipp Zabel <p.zabel@xxxxxxxxxxxxxx> wrote: > > Am Freitag, den 21.10.2016, 13:45 +0800 schrieb Ying Liu: > >> On Thu, Oct 20, 2016 at 9:29 PM, Philipp Zabel <p.zabel@xxxxxxxxxxxxxx> wrote: > >> > Am Donnerstag, den 20.10.2016, 16:51 +0800 schrieb Ying Liu: > >> >> >> Does the clip thing potentially change the user's request by force? > >> >> >> For example, the user request an unreasonable big resolution. > >> >> > > >> >> > The user is allowed to ask for destination coordinates extending outside > >> >> > the crtc dimensions. This will chop off the parts that aren't visible, > >> >> > and it will chop off the corresponding areas of the source as well. > >> >> > >> >> How about returning -EINVAL in this case which stands for > >> >> an atomic check failure? > >> > > >> > Say the user requests to display a 640x480+0,0 source framebuffer at > >> > destination offset -320,0 on a 320x240 screen, unscaled. The expectation > >> > would be to see the upper right quarter of the framebuffer on the > >> > screen, at least if the hardware was actually able to position overlays > >> > partially offscreen. > >> > If we can also fulfill that expectation by clipping the source rectangle > >> > to 320,240+320,0 and changing the destination rectangle to 320x240+0,0, > >> > why should -EINVAL be returned? > >> > >> Well, IIUC, there are two kinds of clipping. > >> 1) Clipping a rectangle from a fb according to src_x/y and src_w/h. > >> 2) Clipping done by drm_plane_helper_check_state(), which potentially > >> changes src/dst->x1/2 and src/dst->y1/2(in other words, src_x/y, > >> src_w/h and crtc_x/y/w/h, though not directly). > >> > >> 1) is fine, no problem. > >> I doubt 2) is wrong as the users' original request could be changed. > >> That's why I mentioned returning -EINVAL. > >> > >> Moreover, before and after applying the patch, I think the > >> ->atomic_check behavior consistency is broken. For example, > >> negative crtc_x or crtc_y for overlay are changed from unacceptable > >> to potentially acceptable just because 2) may change their equivalent > >> dst_>x/y1. > > > > I fail to see what's wrong with 2) as long as we can keep the observable > > behaviour exactly the same as if the user request was unchanged. > > It seems the behavior could change - negative crtc_x or crtc_y for > overlay make ->atomic_check return -EINVAL before(overlay hw state > machine has nothing changed), and potentially successful after(overlay > hw state machine changes). That in itself doesn't seem so bad. One thing we can't do though is 'position' at any negative crtc_x/y due to the fact that when clipping the src.x1/y1 still must be even for chroma subsampled pixel formats and the x1 still must result in scanline start addresses aligned to 8-byte boundaries. So for 32-bit framebuffer depth negative x offsets must be even, and for 16-bit framebuffer depth only negative x offsets that are a multiple of 4 are possible. regards Philipp _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
