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Tue, 25 Aug 2020 11:06:08 -0400 (EDT) Date: Tue, 25 Aug 2020 17:06:06 +0200 From: Maxime Ripard To: Stefan Wahren Subject: Re: [PATCH v4 29/78] drm/vc4: crtc: Add a delay after disabling the PixelValve output Message-ID: <20200825150606.utlynhzo664bwksy@gilmour.lan> References: <20200729144251.us6a2pgkjjmm53ov@gilmour.lan> MIME-Version: 1.0 In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200825_110614_477916_92B397DB X-CRM114-Status: GOOD ( 20.68 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Tim Gover , Dave Stevenson , LKML , DRI Development , Eric Anholt , bcm-kernel-feedback-list@broadcom.com, linux-arm-kernel@lists.infradead.org, Phil Elwell , Nicolas Saenz Julienne , linux-rpi-kernel@lists.infradead.org Content-Type: multipart/mixed; boundary="===============2679418600900526318==" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org --===============2679418600900526318== Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="gbp4s6jsz2sfula3" Content-Disposition: inline --gbp4s6jsz2sfula3 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Hi Stefan, On Wed, Jul 29, 2020 at 05:50:31PM +0200, Stefan Wahren wrote: > Am 29.07.20 um 16:42 schrieb Maxime Ripard: > > Hi, > > > > On Wed, Jul 29, 2020 at 03:09:21PM +0100, Dave Stevenson wrote: > >> On Wed, 8 Jul 2020 at 18:43, Maxime Ripard wrote: > >>> In order to avoid pixels getting stuck in the (unflushable) FIFO betw= een > >>> the HVS and the PV, we need to add some delay after disabling the PV = output > >>> and before disabling the HDMI controller. 20ms seems to be good enoug= h so > >>> let's use that. > >>> > >>> Signed-off-by: Maxime Ripard > >>> --- > >>> drivers/gpu/drm/vc4/vc4_crtc.c | 2 ++ > >>> 1 file changed, 2 insertions(+) > >>> > >>> diff --git a/drivers/gpu/drm/vc4/vc4_crtc.c b/drivers/gpu/drm/vc4/vc4= _crtc.c > >>> index d0b326e1df0a..7b178d67187f 100644 > >>> --- a/drivers/gpu/drm/vc4/vc4_crtc.c > >>> +++ b/drivers/gpu/drm/vc4/vc4_crtc.c > >>> @@ -403,6 +403,8 @@ static void vc4_crtc_atomic_disable(struct drm_cr= tc *crtc, > >>> ret =3D wait_for(!(CRTC_READ(PV_V_CONTROL) & PV_VCONTROL_VIDE= N), 1); > >>> WARN_ONCE(ret, "Timeout waiting for !PV_VCONTROL_VIDEN\n"); > >>> > >>> + mdelay(20); > >> mdelay for 20ms seems a touch unfriendly as it's a busy wait. Can we > >> not msleep instead? > > Since the timing was fairly critical, sleeping didn't seem like a good > > solution since there's definitely some chance you overshoot and end up > > with a higher time than the one you targeted. >=20 > usleep_range(min, max) isn't a solution? My understanding of usleep_range was that you can still overshoot, even though it's backed by an HR timer so the resolution is not a jiffy. Are we certain that we're going to be in that range? Maxime --gbp4s6jsz2sfula3 Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iHUEABYIAB0WIQRcEzekXsqa64kGDp7j7w1vZxhRxQUCX0Uo3gAKCRDj7w1vZxhR xTjQAQCZiLqHqiPNSDq7T1euBsIbQ+XTGhdLmdnBZbUIO+1VPwEA1z/O7HFK3t4N IhM8AxotumyFnRcchBjauHOWLcdL+Qo= =am4A -----END PGP SIGNATURE----- --gbp4s6jsz2sfula3-- --===============2679418600900526318== Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel --===============2679418600900526318==--