From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thierry Reding Subject: Re: [PATCH 13/21] drm/dp: Do not busy-loop during link training Date: Mon, 2 Sep 2019 12:57:36 +0200 Message-ID: <20190902105736.GA19263@ulmo> References: <20190805122350.8838-1-thierry.reding@gmail.com> <20190805122350.8838-13-thierry.reding@gmail.com> <1565271207.3656.17.camel@pengutronix.de> Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="===============2003791103==" Return-path: Received: from mail-wm1-x344.google.com (mail-wm1-x344.google.com [IPv6:2a00:1450:4864:20::344]) by gabe.freedesktop.org (Postfix) with ESMTPS id DED8789C08 for ; Mon, 2 Sep 2019 10:57:41 +0000 (UTC) Received: by mail-wm1-x344.google.com with SMTP id q19so5263733wmc.3 for ; Mon, 02 Sep 2019 03:57:41 -0700 (PDT) In-Reply-To: <1565271207.3656.17.camel@pengutronix.de> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" To: Philipp Zabel Cc: dri-devel@lists.freedesktop.org List-Id: dri-devel@lists.freedesktop.org --===============2003791103== Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="ew6BAiZeqk4r7MaW" Content-Disposition: inline --ew6BAiZeqk4r7MaW Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Thu, Aug 08, 2019 at 03:33:27PM +0200, Philipp Zabel wrote: > On Mon, 2019-08-05 at 14:23 +0200, Thierry Reding wrote: > > From: Thierry Reding > >=20 > > Use microsecond sleeps for the clock recovery and channel equalization > > delays during link training. The duration of these delays can be from > > 100 us up to 16 ms. It is rude to busy-loop for that amount of time. > >=20 > > While at it, also convert to standard coding style by putting the > > opening braces in a function definition on a new line. > >=20 > > Signed-off-by: Thierry Reding > > --- > > drivers/gpu/drm/drm_dp_helper.c | 30 ++++++++++++++++++------------ > > 1 file changed, 18 insertions(+), 12 deletions(-) > >=20 > > diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_h= elper.c > > index 4112570dbe67..344f887fef2c 100644 > > --- a/drivers/gpu/drm/drm_dp_helper.c > > +++ b/drivers/gpu/drm/drm_dp_helper.c > > @@ -120,33 +120,39 @@ u8 drm_dp_get_adjust_request_pre_emphasis(const u= 8 link_status[DP_LINK_STATUS_SI > > } > > EXPORT_SYMBOL(drm_dp_get_adjust_request_pre_emphasis); > > =20 > > -void drm_dp_link_train_clock_recovery_delay(const u8 dpcd[DP_RECEIVER_= CAP_SIZE]) { > > - int rd_interval =3D dpcd[DP_TRAINING_AUX_RD_INTERVAL] & > > - DP_TRAINING_AUX_RD_MASK; > > +void drm_dp_link_train_clock_recovery_delay(const u8 dpcd[DP_RECEIVER_= CAP_SIZE]) > > +{ > > + unsigned int rd_interval =3D dpcd[DP_TRAINING_AUX_RD_INTERVAL] & > > + DP_TRAINING_AUX_RD_MASK; > > =20 > > if (rd_interval > 4) > > - DRM_DEBUG_KMS("AUX interval %d, out of range (max 4)\n", > > + DRM_DEBUG_KMS("AUX interval %u, out of range (max 4)\n", > > rd_interval); > > =20 > > if (rd_interval =3D=3D 0 || dpcd[DP_DPCD_REV] >=3D DP_DPCD_REV_14) > > - udelay(100); > > + rd_interval =3D 100; > > else > > - mdelay(rd_interval * 4); >=20 > rd_interval was in units of 4 ms. >=20 > > + rd_interval *=3D 4; >=20 > This should be *=3D 4000 since the result is fed into usleep_range instead > of mdelay. Good catch! Fixed in v2. >=20 > > + > > + usleep_range(rd_interval, rd_interval * 2); > > } > > EXPORT_SYMBOL(drm_dp_link_train_clock_recovery_delay); > > =20 > > -void drm_dp_link_train_channel_eq_delay(const u8 dpcd[DP_RECEIVER_CAP_= SIZE]) { > > - int rd_interval =3D dpcd[DP_TRAINING_AUX_RD_INTERVAL] & > > - DP_TRAINING_AUX_RD_MASK; > > +void drm_dp_link_train_channel_eq_delay(const u8 dpcd[DP_RECEIVER_CAP_= SIZE]) > > +{ > > + unsigned int rd_interval =3D dpcd[DP_TRAINING_AUX_RD_INTERVAL] & > > + DP_TRAINING_AUX_RD_MASK; > > =20 > > if (rd_interval > 4) > > - DRM_DEBUG_KMS("AUX interval %d, out of range (max 4)\n", > > + DRM_DEBUG_KMS("AUX interval %u, out of range (max 4)\n", > > rd_interval); > > =20 > > if (rd_interval =3D=3D 0) > > - udelay(400); > > + rd_interval =3D 400; > > else > > - mdelay(rd_interval * 4); > > + rd_interval *=3D 4; >=20 > Same as above. Fixed in v2. 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