xserver: Branch 'master'

[GitLab Mirror]

 glamor/glamor_egl.c |   10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

New commits:
commit 7c63c582a17b206a33b57a70dd61e7919a6ef9fe
Author: Mario Kleiner <mario.kleiner.de at gmail.com>
Date:   Thu Aug 26 17:06:49 2021 +0200

    Revert "glamor: Enable modifier support for xfree86 too"
    
    This reverts commit 9b8999411033c9473cd68e92e4690a91aecf5b95.
    
    Turns out that defaulting glamor_egl->dmabuf_capable = TRUE
    breaks kms page-flipping on various Mesa+Linux/DRM-KMS+hardware
    combos, resulting in broken presentation timing, degraded performance
    and awful tearing. E.g., my testing shows that X-Server master +
    Mesa 21.2 + Linux 5.3 on Intel Kabylake has broken pageflipping.
    Similar behaviour was observed in the past on RaspberryPi 4/400
    with VideoCore-6 by myself and others, and iirc by myself on some
    AMD gpu's, although my memories of the latter are a bit dim.
    
    Cfe. https://gitlab.freedesktop.org/mesa/mesa/-/issues/3601 and
    possibly https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/254
    for related problems.
    
    The reason for pageflip failure on the modesetting-ddx under
    DRI3/Present seems to be the following sequence:
    
    1. Atomic modesetting for the modesetting-ddx is broken and therefore
       both disabled by default in the modesetting-ddx itself and also
       force-disabled by the Linux kernel since quite a while. If the kernel
       detects drmSetClientCap(fd, DRM_CLIENT_CAP_ATOMIC, 1); from the
       X-Server, it will reject the request, as a countermeasure to all the
       past and current brokeness.
    
    2. Without DRM_CLIENT_CAP_ATOMIC we don't get the implied universal
       planes support (DRM_CLIENT_CAP_UNIVERSAL_PLANES).
    
    3. Without DRM_CLIENT_CAP_UNIVERSAL_PLANES, drmModeGetPlaneResources()
       will only return overlay planes, but not primary- or cursor planes.
    
    4. As modesetting-ddx drmmode_crtc_create_planes() function can only
       operate on primary planes, but can't get any from drmModeGetPlaneResources(),
       the drmmode_crtc_create_planes() mostly turns into a no-op, never
       executes populate_format_modifiers() and therefore the Linux kernels
       DRM-KMS driver is not ever queried for the list of scanout/pageflip
       capable DRM format modifiers. Iow. the drmmode_crtc->formats[i].modifiers
       list stays empty with zero drmmode_crtc->formats[i].num_modifiers.
    
    5. The list from step 4 provides the format+modifiers for intersection
       which would get returned by the X-Servers DRI3 backend as response to
       a xcb_dri3_get_supported_modifiers_window_modifiers() request. Given
       an empty list was returned in step 4, this will lead to return of an
       empty modifiers list by xcb_dri3_get_supported_modifiers_window_modifiers().
    
    6. Both Mesa's DRI3/Present OpenGL backbuffer allocation logic and iirc
       Mesa/Vulkan/WSI/X11's swapchain image allocation logic use the list
       from xcb_dri3_get_supported_modifiers_window_modifiers() for format+
       modifier selection for scanout/pageflip capable buffers. Cfe. Mesa's
       dri3_alloc_render_buffer() function.
    
       Due to the empty list, the Mesa code falls back to the format+modifiers
       reported by xcb_dri3_get_supported_modifiers_screen_modifiers()
       instead. This list contains all modifiers reported by GLAMOR as
       result of glamor_get_formats() and glamor_get_modifiers(), which
       in turn are query results from Mesa eglQueryDmaBufFormatsEXT()
       and eglQueryDmaBufModifiersEXT(). Iow. all format+modifiers which
       are supported for rendering are considered for the OpenGL backbuffers
       and Vulkan swapchain buffers.
    
    7. Depending on kms driver + gpu combo and Mesa version, such buffers
       are often not direct-scanout / pageflip capable, and so pageflipping
       can't be used for DRI3/Present of fullscreen windows. Whenever the
       system has to fallback to copies instead of pageflips, the results
       are broken presentation timing, degraded performance and quite
       horrible tearing, as the current DRI3/Present implementation does not
       perform any hardware synchronization of copy presents to the start
       of vblank or similar.
    
    By defaulting glamor_egl->dmabuf_capable = FALSE instead, as the server
    1.20 branch does, we avoid this failure:
    
    1. glamor_get_modifiers() turns into a no-op and returns false, not
       reporting any supported dmabuf modifiers to the servers DRI3 code,
       ie. the servers cache_formats_and_modifiers() function can't retrieve
       and cache any format+modifiers. Therefore the servers DRI3 code now
       also reports an empty format+modifiers list when Mesa does a
       xcb_dri3_get_supported_modifiers_screen_modifiers() query.
    
    2. Mesa's buffer allocation code therefore falls back to using the old
       DRI image extensions createImage() function to allocate buffers
       with use flags __DRI_IMAGE_USE_SCANOUT | __DRI_IMAGE_USE_BACKBUFFER
       and our OpenGL backbuffers / Vulkan swapchain images get allocated
       in a direct-scanout / pageflip capable format. Pageflipping works,
       timing and performance is good, presentation is tear-free.
    
    Please consider merging this for branching the X-Server 1.21 branch.
    
    Signed-off-by: Mario Kleiner <mario.kleiner.de at gmail.com>

diff --git a/glamor/glamor_egl.c b/glamor/glamor_egl.c
index 91c36a361..6e0fc6596 100644
--- a/glamor/glamor_egl.c
+++ b/glamor/glamor_egl.c
@@ -1090,11 +1090,11 @@ glamor_egl_init(ScrnInfoPtr scrn, int fd)
                                 "EGL_EXT_image_dma_buf_import") &&
         epoxy_has_egl_extension(glamor_egl->display,
                                 "EGL_EXT_image_dma_buf_import_modifiers")) {
-       if (xf86Info.debug != NULL)
-           glamor_egl->dmabuf_capable = !!strstr(xf86Info.debug,
-                                                "dmabuf_capable");
-       else
-           glamor_egl->dmabuf_capable = TRUE;
+        if (xf86Info.debug != NULL)
+            glamor_egl->dmabuf_capable = !!strstr(xf86Info.debug,
+                                                  "dmabuf_capable");
+        else
+            glamor_egl->dmabuf_capable = FALSE;
     }
 #endif