1. 27 Aug, 2019 12 commits
  2. 26 Aug, 2019 1 commit
    • Lyude Paul's avatar
      drm/i915: Call dma_set_max_seg_size() in i915_driver_hw_probe() · acd674af
      Lyude Paul authored
      Currently, we don't call dma_set_max_seg_size() for i915 because we
      intentionally do not limit the segment length that the device supports.
      However, this results in a warning being emitted if we try to map
      anything larger than SZ_64K on a kernel with CONFIG_DMA_API_DEBUG_SG
      enabled:
      
      [    7.751926] DMA-API: i915 0000:00:02.0: mapping sg segment longer
      than device claims to support [len=98304] [max=65536]
      [    7.751934] WARNING: CPU: 5 PID: 474 at kernel/dma/debug.c:1220
      debug_dma_map_sg+0x20f/0x340
      
      This was originally brought up on
      https://bugs.freedesktop.org/show_bug.cgi?id=108517 , and the consensus
      there was it wasn't really useful to set a limit (and that dma-debug
      isn't really all that useful for i915 in the first place). Unfortunately
      though, CONFIG_DMA_API_DEBUG_SG is enabled in the debug configs for
      various distro kernels. Since a WARN_ON() will disable automatic problem
      reporting (and cause any CI with said option enabled to start
      complaining), we really should just fix the problem.
      
      Note that as me and Chris Wilson discussed, the other solution for this
      would be to make DMA-API not make such assumptions when a driver hasn't
      explicitly set a maximum segment size. But, taking a look at the commit
      which originally introduced this behavior, commit 78c47830
      ("dma-debug: check scatterlist segments"), there is an explicit mention
      of this assumption and how it applies to devices with no segment size:
      
      	Conversely, devices which are less limited than the rather
      	conservative defaults, or indeed have no limitations at all
      	(e.g. GPUs with their own internal MMU), should be encouraged to
      	set appropriate dma_parms, as they may get more efficient DMA
      	mapping performance out of it.
      
      So unless there's any concerns (I'm open to discussion!), let's just
      follow suite and call dma_set_max_seg_size() with UINT_MAX as our limit
      to silence any warnings.
      
      Changes since v3:
      * Drop patch for enabling CONFIG_DMA_API_DEBUG_SG in CI. It looks like
        just turning it on causes the kernel to spit out bogus WARN_ONs()
        during some igt tests which would otherwise require teaching igt to
        disable the various DMA-API debugging options causing this. This is
        too much work to be worth it, since DMA-API debugging is useless for
        us. So, we'll just settle with this single patch to squelch WARN_ONs()
        during driver load for users that have CONFIG_DMA_API_DEBUG_SG turned
        on for some reason.
      * Move dma_set_max_seg_size() call into i915_driver_hw_probe() - Chris
        Wilson
      Signed-off-by: default avatarLyude Paul <lyude@redhat.com>
      Reviewed-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
      Cc: <stable@vger.kernel.org> # v4.18+
      Link: https://patchwork.freedesktop.org/patch/msgid/20190823205251.14298-1-lyude@redhat.com
      acd674af
  3. 24 Aug, 2019 2 commits
  4. 23 Aug, 2019 23 commits
  5. 22 Aug, 2019 2 commits