drm/udl: Untangle .get_modes() and .detect_ctx()

Provide separate implementations of .get_modes() and .detect_ctx()
from struct drm_connector. Switch to struct drm_edid.

Udl's .detect() helper used to fetch the EDID from the adapter and the
.get_modes() helper provided display modes from the data. But this
relied on the DRM helpers to call the functions in the correct order.
When no EDID could be retrieved, .detect() regularly printed a warning
to the kernel log.

Switching to the new helpers around struct drm_edid separates both from
each other. The .get_modes() helper now fetches the EDID by itself and
the .detect_ctx() helper only tests for its presence. The patch does a
number of things to implement this.

- Move udl_get_edid_block() to udl_edid.c and rename it to
udl_read_edid_block(). Then use the helper to implement probing in
udl_probe_edid() and reading in udl_edid_read(). The latter helper
is build on top of DRM helpers.

- Replace the existing code in .get_modes() and .detect() with udl's
new EDID helpers. The new code behaves like DRM's similar DDC-based
helpers. Instead of .detect(), udl now implements .detect_ctx().

- Remove the edid data from struct udl_connector. The field cached
the EDID data between calls to .detect() and .get_modes(), but is now
unused.

v3:
- implement udl_probe_edid() with memchr_inv() (Jani)

v2:
- implement udl_probe_edid() within udl
- reword commit description
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240510154841.11370-5-tzimmermann@suse.de

drivers/gpu/drm/udl/Makefile

@@ -2,6 +2,7 @@
 
 udl-y := \
 	udl_drv.o \
+	udl_edid.o \
 	udl_main.o \
 	udl_modeset.o \
 	udl_transfer.o

drivers/gpu/drm/udl/udl_drv.h

@@ -51,8 +51,6 @@ struct urb_list {
 
 struct udl_connector {
 	struct drm_connector connector;
-	/* last udl_detect edid */
-	struct edid *edid;
 };
 
 static inline struct udl_connector *to_udl_connector(struct drm_connector *connector)

drivers/gpu/drm/udl/udl_edid.c

+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <linux/string.h>
+
+#include <drm/drm_drv.h>
+#include <drm/drm_edid.h>
+
+#include "udl_drv.h"
+#include "udl_edid.h"
+
+static int udl_read_edid_block(void *data, u8 *buf, unsigned int block, size_t len)
+{
+	struct udl_device *udl = data;
+	struct drm_device *dev = &udl->drm;
+	struct usb_device *udev = udl_to_usb_device(udl);
+	u8 *read_buff;
+	int idx, ret;
+	size_t i;
+
+	read_buff = kmalloc(2, GFP_KERNEL);
+	if (!read_buff)
+		return -ENOMEM;
+
+	if (!drm_dev_enter(dev, &idx)) {
+		ret = -ENODEV;
+		goto err_kfree;
+	}
+
+	for (i = 0; i < len; i++) {
+		int bval = (i + block * EDID_LENGTH) << 8;
+
+		ret = usb_control_msg(udev, usb_rcvctrlpipe(udev, 0),
+				      0x02, (0x80 | (0x02 << 5)), bval,
+				      0xA1, read_buff, 2, USB_CTRL_GET_TIMEOUT);
+		if (ret < 0) {
+			drm_err(dev, "Read EDID byte %zu failed err %x\n", i, ret);
+			goto err_drm_dev_exit;
+		} else if (ret < 1) {
+			ret = -EIO;
+			drm_err(dev, "Read EDID byte %zu failed\n", i);
+			goto err_drm_dev_exit;
+		}
+
+		buf[i] = read_buff[1];
+	}
+
+	drm_dev_exit(idx);
+	kfree(read_buff);
+
+	return 0;
+
+err_drm_dev_exit:
+	drm_dev_exit(idx);
+err_kfree:
+	kfree(read_buff);
+	return ret;
+}
+
+bool udl_probe_edid(struct udl_device *udl)
+{
+	u8 hdr[8];
+	int ret;
+
+	ret = udl_read_edid_block(udl, hdr, 0, sizeof(hdr));
+	if (ret)
+		return false;
+
+	/*
+	 * The adapter sends all-zeros if no monitor has been
+	 * connected. We consider anything else a connection.
+	 */
+	return !!memchr_inv(hdr, 0, sizeof(hdr));
+}
+
+const struct drm_edid *udl_edid_read(struct drm_connector *connector)
+{
+	struct udl_device *udl = to_udl(connector->dev);
+
+	return drm_edid_read_custom(connector, udl_read_edid_block, udl);
+}

drivers/gpu/drm/udl/udl_edid.h

+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#ifndef UDL_EDID_H
+#define UDL_EDID_H
+
+#include <linux/types.h>
+
+struct drm_connector;
+struct drm_edid;
+struct udl_device;
+
+bool udl_probe_edid(struct udl_device *udl);
+const struct drm_edid *udl_edid_read(struct drm_connector *connector);
+
+#endif

drivers/gpu/drm/udl/udl_modeset.c

@@ -25,6 +25,7 @@
 #include <drm/drm_vblank.h>
 
 #include "udl_drv.h"
+#include "udl_edid.h"
 #include "udl_proto.h"
 
 /*
@@ -415,97 +416,44 @@ static const struct drm_encoder_funcs udl_encoder_funcs = {
 
 static int udl_connector_helper_get_modes(struct drm_connector *connector)
 {
-	struct udl_connector *udl_connector = to_udl_connector(connector);
+	const struct drm_edid *drm_edid;
+	int count;
 
-	drm_connector_update_edid_property(connector, udl_connector->edid);
-	if (udl_connector->edid)
-		return drm_add_edid_modes(connector, udl_connector->edid);
+	drm_edid = udl_edid_read(connector);
+	drm_edid_connector_update(connector, drm_edid);
+	count = drm_edid_connector_add_modes(connector);
+	drm_edid_free(drm_edid);
 
-	return 0;
+	return count;
 }
 
-static const struct drm_connector_helper_funcs udl_connector_helper_funcs = {
-	.get_modes = udl_connector_helper_get_modes,
-};
-
-static int udl_get_edid_block(void *data, u8 *buf, unsigned int block, size_t len)
+static int udl_connector_helper_detect_ctx(struct drm_connector *connector,
+					   struct drm_modeset_acquire_ctx *ctx,
+					   bool force)
 {
-	struct udl_device *udl = data;
-	struct drm_device *dev = &udl->drm;
-	struct usb_device *udev = udl_to_usb_device(udl);
-	u8 *read_buff;
-	int idx, ret;
-	size_t i;
-
-	read_buff = kmalloc(2, GFP_KERNEL);
-	if (!read_buff)
-		return -ENOMEM;
-
-	if (!drm_dev_enter(dev, &idx)) {
-		ret = -ENODEV;
-		goto err_kfree;
-	}
-
-	for (i = 0; i < len; i++) {
-		int bval = (i + block * EDID_LENGTH) << 8;
-
-		ret = usb_control_msg(udev, usb_rcvctrlpipe(udev, 0),
-				      0x02, (0x80 | (0x02 << 5)), bval,
-				      0xA1, read_buff, 2, USB_CTRL_GET_TIMEOUT);
-		if (ret < 0) {
-			drm_err(dev, "Read EDID byte %zu failed err %x\n", i, ret);
-			goto err_drm_dev_exit;
-		} else if (ret < 1) {
-			ret = -EIO;
-			drm_err(dev, "Read EDID byte %zu failed\n", i);
-			goto err_drm_dev_exit;
-		}
-
-		buf[i] = read_buff[1];
-	}
-
-	drm_dev_exit(idx);
-	kfree(read_buff);
+	struct udl_device *udl = to_udl(connector->dev);
 
-	return 0;
+	if (udl_probe_edid(udl))
+		return connector_status_connected;
 
-err_drm_dev_exit:
-	drm_dev_exit(idx);
-err_kfree:
-	kfree(read_buff);
-	return ret;
+	return connector_status_disconnected;
 }
 
-static enum drm_connector_status udl_connector_detect(struct drm_connector *connector, bool force)
-{
-	struct drm_device *dev = connector->dev;
-	struct udl_device *udl = to_udl(dev);
-	struct udl_connector *udl_connector = to_udl_connector(connector);
-	enum drm_connector_status status = connector_status_disconnected;
-
-	/* cleanup previous EDID */
-	kfree(udl_connector->edid);
-	udl_connector->edid = NULL;
-
-	udl_connector->edid = drm_do_get_edid(connector, udl_get_edid_block, udl);
-	if (udl_connector->edid)
-		status = connector_status_connected;
-
-	return status;
-}
+static const struct drm_connector_helper_funcs udl_connector_helper_funcs = {
+	.get_modes = udl_connector_helper_get_modes,
+	.detect_ctx = udl_connector_helper_detect_ctx,
+};
 
 static void udl_connector_destroy(struct drm_connector *connector)
 {
 	struct udl_connector *udl_connector = to_udl_connector(connector);
 
 	drm_connector_cleanup(connector);
-	kfree(udl_connector->edid);
 	kfree(udl_connector);
 }
 
 static const struct drm_connector_funcs udl_connector_funcs = {
 	.reset = drm_atomic_helper_connector_reset,
-	.detect = udl_connector_detect,
 	.fill_modes = drm_helper_probe_single_connector_modes,
 	.destroy = udl_connector_destroy,
 	.atomic_duplicate_state = drm_atomic_helper_connector_duplicate_state,