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[10.160.88.99]) by sjmaillnx1.cadence.com (8.14.4/8.14.4) with ESMTP id x0UB4Xif009639 (version=TLSv1/SSLv3 cipher=AES256-SHA bits=256 verify=OK); Wed, 30 Jan 2019 03:04:34 -0800 X-CrossPremisesHeadersFilteredBySendConnector: maileu3.global.cadence.com Received: from maileu3.global.cadence.com (10.160.88.99) by maileu3.global.cadence.com (10.160.88.99) with Microsoft SMTP Server (TLS) id 15.0.1367.3; Wed, 30 Jan 2019 12:04:31 +0100 Received: from lvloginb.cadence.com (10.165.177.11) by maileu3.global.cadence.com (10.160.88.99) with Microsoft SMTP Server (TLS) id 15.0.1367.3 via Frontend Transport; Wed, 30 Jan 2019 12:04:31 +0100 Received: from lvloginb.cadence.com (localhost [127.0.0.1]) by lvloginb.cadence.com (8.14.4/8.14.4) with ESMTP id x0UB4VbI018087; Wed, 30 Jan 2019 11:04:31 GMT Received: (from dkos@localhost) by lvloginb.cadence.com (8.14.4/8.14.4/Submit) id x0UB4Uj5018077; Wed, 30 Jan 2019 11:04:30 GMT From: Damian Kos To: David Airlie , Daniel Vetter , "Rob Herring" , Mark Rutland , "Andrzej Hajda" , Laurent Pinchart , Maarten Lankhorst , Maxime Ripard , Sean Paul , Sandy Huang , =?UTF-8?q?Heiko=20St=C3=BCbner?= , , , , , CC: , , , , , Quentin Schulz Subject: [PATCH v7 2/4] drm/dp: fix link probing for devices supporting DP 1.4+ Date: Wed, 30 Jan 2019 11:03:19 +0000 Message-ID: <1548846209-16406-3-git-send-email-dkos@cadence.com> X-Mailer: git-send-email 1.9.0 In-Reply-To: <1548846209-16406-1-git-send-email-dkos@cadence.com> References: <1548846209-16406-1-git-send-email-dkos@cadence.com> MIME-Version: 1.0 Content-Type: text/plain X-OrganizationHeadersPreserved: maileu3.global.cadence.com X-EOPAttributedMessage: 0 X-Forefront-Antispam-Report: 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include:auth.msgapp.com include:spf.mandrillapp.com ~all X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-01-30_08:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_check_notspam policy=outbound_check score=0 priorityscore=1501 malwarescore=0 suspectscore=2 phishscore=0 bulkscore=0 spamscore=0 clxscore=1011 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=748 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1901300089 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Quentin Schulz DP 1.4 introduced a DP_EXTENDED_RECEIVER_CAP_FIELD_PRESENT bit in DP_TRAINING_AUX_RD_INTERVAL register. If set, DPCD registers from DP_DPCD_REV to DP_ADAPTER_CAP should be retrieved starting from DP_DPCD_REV_EXTENDED. All registers are copied except DP_DPCD_REV, DP_MAX_LINK_RATE and DP_DOWNSTREAMPORT_PRESENT which represent the "true capabilities" of DPRX device. Original DP_DPCD_REV, DP_MAX_LINK_RATE and DP_DOWNSTREAMPORT_PRESENT might falsely return lower capabilities to "avoid interoperability issues with some of the existing DP Source devices that malfunction when they discover the higher capabilities within those three registers.". Before DP 1.4, DP_EXTENDED_RECEIVER_CAP_FIELD_PRESENT bit was reserved and read 0 so it's safe to check against it even if DP revision is <1.4 Signed-off-by: Quentin Schulz Signed-off-by: Damian Kos Reviewed-by: Andrzej Hajda Reviewed-by: Manasi Navare --- drivers/gpu/drm/drm_dp_helper.c | 30 +++++++++++++++++++++++++++++- 1 file changed, 29 insertions(+), 1 deletion(-) diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c index 54120b6319e7..4e36d708fdce 100644 --- a/drivers/gpu/drm/drm_dp_helper.c +++ b/drivers/gpu/drm/drm_dp_helper.c @@ -372,10 +372,38 @@ int drm_dp_link_probe(struct drm_dp_aux *aux, struct drm_dp_link *link) { u8 values[3]; int err; + unsigned int addr; memset(link, 0, sizeof(*link)); - err = drm_dp_dpcd_read(aux, DP_DPCD_REV, values, sizeof(values)); + /* + * DP 1.4 introduced a DP_EXTENDED_RECEIVER_CAP_FIELD_PRESENT bit in + * DP_TRAINING_AUX_RD_INTERVAL register. If set, DPCD registers from + * DP_DPCD_REV to DP_ADAPTER_CAP should be retrieved starting from + * DP_DPCD_REV_EXTENDED. All registers are copied except DP_DPCD_REV, + * DP_MAX_LINK_RATE and DP_DOWNSTREAMPORT_PRESENT which represent the + * "true capabilities" of DPRX device. + * + * Original DP_DPCD_REV, DP_MAX_LINK_RATE and DP_DOWNSTREAMPORT_PRESENT + * might falsely return lower capabilities to "avoid interoperability + * issues with some of the existing DP Source devices that malfunction + * when they discover the higher capabilities within those three + * registers.". + * + * Before DP 1.4, DP_EXTENDED_RECEIVER_CAP_FIELD_PRESENT bit was + * reserved and read 0 so it's safe to check against it even if + * DP revision is <1.4 + */ + err = drm_dp_dpcd_readb(aux, DP_TRAINING_AUX_RD_INTERVAL, values); + if (err < 0) + return err; + + if (values[0] & DP_EXTENDED_RECEIVER_CAP_FIELD_PRESENT) + addr = DP_DP13_DPCD_REV; + else + addr = DP_DPCD_REV; + + err = drm_dp_dpcd_read(aux, addr, values, sizeof(values)); if (err < 0) return err; -- 2.17.1