[RFC 13/20] drm/i915/dp: Extract drm_dp_downstream_read_info()

From: Lyude Paul <lyude@redhat.com>
To: nouveau@lists.freedesktop.org, intel-gfx@lists.freedesktop.org,
	dri-devel@lists.freedesktop.org
Cc: "Maarten Lankhorst" <maarten.lankhorst@linux.intel.com>,
	"Maxime Ripard" <mripard@kernel.org>,
	"Thomas Zimmermann" <tzimmermann@suse.de>,
	"David Airlie" <airlied@linux.ie>,
	"Daniel Vetter" <daniel@ffwll.ch>,
	"Jani Nikula" <jani.nikula@linux.intel.com>,
	"Joonas Lahtinen" <joonas.lahtinen@linux.intel.com>,
	"Rodrigo Vivi" <rodrigo.vivi@intel.com>,
	"Ville Syrjälä" <ville.syrjala@linux.intel.com>,
	"José Roberto de Souza" <jose.souza@intel.com>,
	"Manasi Navare" <manasi.d.navare@intel.com>,
	"Uma Shankar" <uma.shankar@intel.com>,
	"Gwan-gyeong Mun" <gwan-gyeong.mun@intel.com>,
	"Imre Deak" <imre.deak@intel.com>,
	"Wambui Karuga" <wambui.karugax@gmail.com>,
	"Lucas De Marchi" <lucas.demarchi@intel.com>,
	linux-kernel@vger.kernel.org (open list)
Subject: [RFC 13/20] drm/i915/dp: Extract drm_dp_downstream_read_info()
Date: Tue, 11 Aug 2020 16:04:50 -0400	[thread overview]
Message-ID: <20200811200457.134743-14-lyude@redhat.com> (raw)
In-Reply-To: <20200811200457.134743-1-lyude@redhat.com>

We're going to be doing the same probing process in nouveau for
determining downstream DP port capabilities, so let's deduplicate the
work by moving i915's code for handling this into a shared helper:
drm_dp_downstream_read_info().

Note that when we do this, we also do make some functional changes while
we're at it:
* We always clear the downstream port info before trying to read it,
  just to make things easier for the caller
* We skip reading downstream port info if the DPCD indicates that we
  don't support downstream port info
* We only read as many bytes as needed for the reported number of
  downstream ports, no sense in reading the whole thing every time

Signed-off-by: Lyude Paul <lyude@redhat.com>
---
 drivers/gpu/drm/drm_dp_helper.c         | 32 +++++++++++++++++++++++++
 drivers/gpu/drm/i915/display/intel_dp.c | 14 ++---------
 include/drm/drm_dp_helper.h             |  3 +++
 3 files changed, 37 insertions(+), 12 deletions(-)

diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index 4c21cf69dad5a..9703b33599c3b 100644
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/drivers/gpu/drm/drm_dp_helper.c
@@ -423,6 +423,38 @@ bool drm_dp_send_real_edid_checksum(struct drm_dp_aux *aux,
 }
 EXPORT_SYMBOL(drm_dp_send_real_edid_checksum);
 
+/**
+ * drm_dp_downstream_read_info() - read DPCD downstream port info if available
+ * @aux: DisplayPort AUX channel
+ * @dpcd: A cached copy of the port's DPCD
+ * @downstream_ports: buffer to store the downstream port info in
+ *
+ * Returns: 0 if either the downstream port info was read successfully or
+ * there was no downstream info to read, or a negative error code otherwise.
+ */
+int drm_dp_downstream_read_info(struct drm_dp_aux *aux,
+				const u8 dpcd[DP_RECEIVER_CAP_SIZE],
+				u8 downstream_ports[DP_MAX_DOWNSTREAM_PORTS])
+{
+	int ret;
+	u8 len;
+
+	memset(downstream_ports, 0, DP_MAX_DOWNSTREAM_PORTS);
+
+	/* No downstream info to read */
+	if (!drm_dp_is_branch(dpcd) ||
+	    dpcd[DP_DPCD_REV] < DP_DPCD_REV_10 ||
+	    !(dpcd[DP_DOWNSTREAMPORT_PRESENT] & DP_DWN_STRM_PORT_PRESENT))
+		return 0;
+
+	len = (dpcd[DP_DOWN_STREAM_PORT_COUNT] & DP_PORT_COUNT_MASK) * 4;
+	ret = drm_dp_dpcd_read(aux, DP_DOWNSTREAM_PORT_0, downstream_ports,
+			       len);
+
+	return ret == len ? 0 : -EIO;
+}
+EXPORT_SYMBOL(drm_dp_downstream_read_info);
+
 /**
  * drm_dp_downstream_max_clock() - extract branch device max
  *                                 pixel rate for legacy VGA
diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
index 1e29d3a012856..984e49194ca31 100644
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -4685,18 +4685,8 @@ intel_dp_get_dpcd(struct intel_dp *intel_dp)
 			return false;
 	}
 
-	if (!drm_dp_is_branch(intel_dp->dpcd))
-		return true; /* native DP sink */
-
-	if (intel_dp->dpcd[DP_DPCD_REV] == 0x10)
-		return true; /* no per-port downstream info */
-
-	if (drm_dp_dpcd_read(&intel_dp->aux, DP_DOWNSTREAM_PORT_0,
-			     intel_dp->downstream_ports,
-			     DP_MAX_DOWNSTREAM_PORTS) < 0)
-		return false; /* downstream port status fetch failed */
-
-	return true;
+	return drm_dp_downstream_read_info(&intel_dp->aux, intel_dp->dpcd,
+					   intel_dp->downstream_ports) == 0;
 }
 
 static bool
diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
index 5c28199248626..1349f16564ace 100644
--- a/include/drm/drm_dp_helper.h
+++ b/include/drm/drm_dp_helper.h
@@ -1613,6 +1613,9 @@ int drm_dp_dpcd_read_link_status(struct drm_dp_aux *aux,
 bool drm_dp_send_real_edid_checksum(struct drm_dp_aux *aux,
 				    u8 real_edid_checksum);
 
+int drm_dp_downstream_read_info(struct drm_dp_aux *aux,
+				const u8 dpcd[DP_RECEIVER_CAP_SIZE],
+				u8 downstream_ports[DP_MAX_DOWNSTREAM_PORTS]);
 int drm_dp_downstream_max_clock(const u8 dpcd[DP_RECEIVER_CAP_SIZE],
 				const u8 port_cap[4]);
 int drm_dp_downstream_max_bpc(const u8 dpcd[DP_RECEIVER_CAP_SIZE],
-- 
2.26.2

