1. 05 May, 2023 1 commit
    • Brian Norris's avatar
      drm/atomic: Allow vblank-enabled + self-refresh "disable" · 9d0e3cac
      Brian Norris authored
      The self-refresh helper framework overloads "disable" to sometimes mean
      "go into self-refresh mode," and this mode activates automatically
      (e.g., after some period of unchanging display output). In such cases,
      the display pipe is still considered "on", and user-space is not aware
      that we went into self-refresh mode. Thus, users may expect that
      vblank-related features (such as DRM_IOCTL_WAIT_VBLANK) still work
      properly.
      
      However, we trigger the WARN_ONCE() here if a CRTC driver tries to leave
      vblank enabled.
      
      Add a different expectation: that CRTCs *should* leave vblank enabled
      when going into self-refresh.
      
      This patch is preparation for another patch -- "drm/rockchip: vop: Leave
      vblank enabled in self-refresh" -- which resolves conflicts between the
      above self-refresh behavior and the API tests in IGT's kms_vblank test
      module.
      
      == Some alternatives discussed: ==
      
      It's likely that on many display controllers, vblank interrupts will
      turn off when the CRTC is disabled, and so in some cases, self-refresh
      may not support vblank. To support such cases, we might consider
      additions to the generic helpers such that we fire vblank events based
      on a timer.
      
      However, there is currently only one driver using the common
      self-refresh helpers (i.e., rockchip), and at least as of commit
      bed030a4 ("drm/rockchip: Don't fully disable vop on self refresh"),
      the CRTC hardware is powered enough to continue to generate vblank
      interrupts.
      
      So we chose the simpler option of leaving vblank interrupts enabled. We
      can reevaluate this decision and perhaps augment the helpers if/when we
      gain a second driver that has different requirements.
      
      v3:
       * include discussion summary
      
      v2:
       * add 'ret != 0' warning case for self-refresh
       * describe failing test case and relation to drm/rockchip patch better
      
      Cc: <stable@vger.kernel.org> # dependency for "drm/rockchip: vop: Leave
                                   # vblank enabled in self-refresh"
      Signed-off-by: default avatarBrian Norris <briannorris@chromium.org>
      Signed-off-by: default avatarSean Paul <seanpaul@chromium.org>
      Link: https://patchwork.freedesktop.org/patch/msgid/20230109171809.v3.1.I3904f697863649eb1be540ecca147a66e42bfad7@changeid
      9d0e3cac
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