[PATCH] drm: avoid spurious EBUSY due to nonblocking atomic modesets

Wed Sep 23 11:31:52 UTC 2020

On Wed, Sep 23, 2020 at 01:16:42PM +0200, Daniel Vetter wrote:
> On Wed, Sep 23, 2020 at 1:14 PM Marius Vlad <marius.vlad at collabora.com> wrote:
> >
> > On Wed, Sep 23, 2020 at 12:58:30PM +0200, Daniel Vetter wrote:
> > > On Tue, Sep 22, 2020 at 3:36 PM Marius Vlad <marius.vlad at collabora.com> wrote:
> > > >
> > > > On Fri, Jan 31, 2020 at 07:34:00AM +0000, Daniel Stone wrote:
> > > > > On Thu, 5 Jul 2018 at 11:21, Daniel Vetter <daniel.vetter at ffwll.ch> wrote:
> > > > > > When doing an atomic modeset with ALLOW_MODESET drivers are allowed to
> > > > > > pull in arbitrary other resources, including CRTCs (e.g. when
> > > > > > reconfiguring global resources).
> > > > > >
> > > > > > But in nonblocking mode userspace has then no idea this happened,
> > > > > > which can lead to spurious EBUSY calls, both:
> > > > > > - when that other CRTC is currently busy doing a page_flip the
> > > > > >   ALLOW_MODESET commit can fail with an EBUSY
> > > > > > - on the other CRTC a normal atomic flip can fail with EBUSY because
> > > > > >   of the additional commit inserted by the kernel without userspace's
> > > > > >   knowledge
> > > > > >
> > > > > > For blocking commits this isn't a problem, because everyone else will
> > > > > > just block until all the CRTC are reconfigured. Only thing userspace
> > > > > > can notice is the dropped frames without any reason for why frames got
> > > > > > dropped.
> > > > > >
> > > > > > Consensus is that we need new uapi to handle this properly, but no one
> > > > > > has any idea what exactly the new uapi should look like. As a stop-gap
> > > > > > plug this problem by demoting nonblocking commits which might cause
> > > > > > issues by including CRTCs not in the original request to blocking
> > > > > > commits.
> > > > Gentle ping. I've tried out Linus's master tree and, and like Pekka,
> > > > I've noticed this isn't integrated/added.
> > > >
> > > > Noticed this is fixing (also) DPMS when multiple outputs are in use.
> > > > Wondering if we can just use a _ONCE() variant instead of WARN_ON(). I'm seeing
> > > > the warning quite often.
> > >
> > > On which driver/chip does this happen?
> > I've tried it out on i915.
> 
> lspci -nn please.
Sure,

$ lspci -nn
00:00.0 Host bridge [0600]: Intel Corporation Xeon E3-1200 v6/7th Gen Core Processor Host Bridge/DRAM Registers [8086:5914] (rev 08)
00:02.0 VGA compatible controller [0300]: Intel Corporation UHD Graphics 620 [8086:5917] (rev 07)
00:04.0 Signal processing controller [1180]: Intel Corporation Xeon E3-1200 v5/E3-1500 v5/6th Gen Core Processor Thermal Subsystem [8086:1903] (rev 08)
00:14.0 USB controller [0c03]: Intel Corporation Sunrise Point-LP USB 3.0 xHCI Controller [8086:9d2f] (rev 21)
00:14.2 Signal processing controller [1180]: Intel Corporation Sunrise Point-LP Thermal subsystem [8086:9d31] (rev 21)
00:15.0 Signal processing controller [1180]: Intel Corporation Sunrise Point-LP Serial IO I2C Controller #0 [8086:9d60] (rev 21)
00:15.1 Signal processing controller [1180]: Intel Corporation Sunrise Point-LP Serial IO I2C Controller #1 [8086:9d61] (rev 21)
00:16.0 Communication controller [0780]: Intel Corporation Sunrise Point-LP CSME HECI #1 [8086:9d3a] (rev 21)
00:1c.0 PCI bridge [0604]: Intel Corporation Sunrise Point-LP PCI Express Root Port #1 [8086:9d10] (rev f1)
00:1c.2 PCI bridge [0604]: Intel Corporation Sunrise Point-LP PCI Express Root Port #3 [8086:9d12] (rev f1)
00:1c.4 PCI bridge [0604]: Intel Corporation Sunrise Point-LP PCI Express Root Port #5 [8086:9d14] (rev f1)
00:1d.0 PCI bridge [0604]: Intel Corporation Sunrise Point-LP PCI Express Root Port #9 [8086:9d18] (rev f1)
00:1f.0 ISA bridge [0601]: Intel Corporation Sunrise Point LPC Controller/eSPI Controller [8086:9d4e] (rev 21)
00:1f.2 Memory controller [0580]: Intel Corporation Sunrise Point-LP PMC [8086:9d21] (rev 21)
00:1f.3 Audio device [0403]: Intel Corporation Sunrise Point-LP HD Audio [8086:9d71] (rev 21)
00:1f.4 SMBus [0c05]: Intel Corporation Sunrise Point-LP SMBus [8086:9d23] (rev 21)
01:00.0 Unassigned class [ff00]: Realtek Semiconductor Co., Ltd. RTS525A PCI Express Card Reader [10ec:525a] (rev 01)
02:00.0 Network controller [0280]: Qualcomm Atheros QCA6174 802.11ac Wireless Network Adapter [168c:003e] (rev 32)
6e:00.0 Non-Volatile memory controller [0108]: Toshiba Corporation Device [1179:0116]

(it's a xps laptop)

> 
> Also adding Ville, who has an idea where this can all go wrong. The
> one he pointed out thus far is gen12+ only though.
> -Daniel
> 
> > > -Daniel
> > >
> > > >
> > > > >
> > > > > Thanks for writing this up Daniel, and for reminding me about it some
> > > > > time later as well ...
> > > > >
> > > > > Reviewed-by: Daniel Stone <daniels at collabora.com>
> > > > >
> > > > > Cheers,
> > > > > Daniel
> > > > > _______________________________________________
> > > > > dri-devel mailing list
> > > > > dri-devel at lists.freedesktop.org
> > > > > https://lists.freedesktop.org/mailman/listinfo/dri-devel
> > >
> > >
> > >
> > > --
> > > Daniel Vetter
> > > Software Engineer, Intel Corporation
> > > http://blog.ffwll.ch
> 
> 
> 
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch
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