Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Tue, 4 Jun 2019 23:45:43 -0300
From:   Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
To:     Simon Ser <simon.ser@intel.com>,
        Ville Syrjala <ville.syrjala@linux.intel.com>,
        Shayenne Moura <shayenneluzmoura@gmail.com>,
        Haneen Mohammed <hamohammed.sa@gmail.com>,
        Daniel Vetter <daniel@ffwll.ch>,
        David Airlie <airlied@linux.ie>
Cc:     dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org,
        18oliveira.charles@gmail.com
Subject: [PATCH V2] drm/vkms: Avoid extra discount in the timestamp value
Message-ID: <20190605024543.pcsnkf74mmgfhtuh@smtp.gmail.com>
MIME-Version: 1.0
Content-Type: multipart/signed; micalg=pgp-sha512;
        protocol="application/pgp-signature"; boundary="fjpgzm34khffs6b6"
Content-Disposition: inline
User-Agent: NeoMutt/20180716
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


--fjpgzm34khffs6b6
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
Content-Transfer-Encoding: quoted-printable

After the commit def35e7c5926 ("drm/vkms: Bugfix extra vblank frame")
some of the crc tests started to fail in the vkms with the following
error:

 [drm:drm_crtc_add_crc_entry [drm]] *ERROR* Overflow of CRC buffer,
    userspace reads too slow.
 [drm] failed to queue vkms_crc_work_handle
 ...

The aforementioned commit fixed the extra vblank added by
`drm_crtc_arm_vblank_event()` which is invoked inside
`vkms_crtc_atomic_flush()` if the vblank event count was zero, otherwise
`drm_crtc_send_vblank_event()` is invoked. The fix was implemented in
`vkms_get_vblank_timestamp()` by subtracting one period from the current
timestamp, as the code snippet below illustrates:

 if (!in_vblank_irq)
  *vblank_time -=3D output->period_ns;

The above fix works well when `drm_crtc_arm_vblank_event()` is invoked.
However, it does not properly work when `drm_crtc_send_vblank_event()`
executes since it subtracts the correct timestamp, which it shouldn't.
In this case, the `drm_crtc_accurate_vblank_count()` function will
returns the wrong frame number, which generates the aforementioned
error. Such decrease in `get_vblank_timestamp()` produce a negative
number in the following calculation within `drm_update_vblank_count()`:

 u64 diff_ns =3D ktime_to_ns(ktime_sub(t_vblank, vblank->time));

After this operation, the DIV_ROUND_CLOSEST_ULL macro is invoked using
diff_ns with a negative number, which generates an undefined result;
therefore, the returned frame is a huge and incorrect number. Finally,
the code below is part of the `vkms_crc_work_handle()`, note that the
while loop depends on the returned value from
`drm_crtc_accurate_vblank_count()` which may cause the loop to take a
long time to finish in case of huge value.

 frame_end =3D drm_crtc_accurate_vblank_count(crtc);
 while (frame_start <=3D frame_end)
   drm_crtc_add_crc_entry(crtc, true, frame_start++, &crc32);

This commit fixes this issue by checking if the vblank timestamp
corresponding to the current software vblank counter is equal to the
current vblank; if they are equal, it means that
`drm_crtc_send_vblank_event()` was invoked and vkms does not need to
discount the extra vblank, otherwise, `drm_crtc_arm_vblank_event()` was
executed and vkms have to discount the extra vblank. This fix made the
CRC tests work again whereas keep all tests from kms_flip working as
well.

V2: Update commit message

Signed-off-by: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
Signed-off-by: Shayenne Moura <shayenneluzmoura@gmail.com>
---
 drivers/gpu/drm/vkms/vkms_crtc.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/vkms/vkms_crtc.c b/drivers/gpu/drm/vkms/vkms_c=
rtc.c
index 7508815fac11..3ce60e66673e 100644
--- a/drivers/gpu/drm/vkms/vkms_crtc.c
+++ b/drivers/gpu/drm/vkms/vkms_crtc.c
@@ -74,9 +74,13 @@ bool vkms_get_vblank_timestamp(struct drm_device *dev, u=
nsigned int pipe,
 {
 	struct vkms_device *vkmsdev =3D drm_device_to_vkms_device(dev);
 	struct vkms_output *output =3D &vkmsdev->output;
+	struct drm_vblank_crtc *vblank =3D &dev->vblank[pipe];
=20
 	*vblank_time =3D output->vblank_hrtimer.node.expires;
=20
+	if (*vblank_time =3D=3D vblank->time)
+		return true;
+
 	if (!in_vblank_irq)
 		*vblank_time -=3D output->period_ns;
=20
--=20
2.21.0


--fjpgzm34khffs6b6
Content-Type: application/pgp-signature; name="signature.asc"

-----BEGIN PGP SIGNATURE-----
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=5usR
-----END PGP SIGNATURE-----

--fjpgzm34khffs6b6--