On Sun, Feb 23, 2020 at 6:43 PM Noralf Trønnes [off-list ref] wrote:

Den 17.02.2020 10.38, skrev Daniel Vetter:

quoted

On Sun, Feb 16, 2020 at 06:21:16PM +0100, Noralf Trønnes wrote:

quoted

drm_client_init_from_id() provides a way for clients to add a client based
on the minor. drm_client_modeset_set() provides a way to set the modeset
for clients that handles connectors and display mode on their own.

Signed-off-by: Noralf Trønnes <redacted>
---
 drivers/gpu/drm/drm_client.c         | 37 ++++++++++++++++++++
 drivers/gpu/drm/drm_client_modeset.c | 52 ++++++++++++++++++++++++++++
 include/drm/drm_client.h             |  4 +++
 3 files changed, 93 insertions(+)

diff --git a/drivers/gpu/drm/drm_client.c b/drivers/gpu/drm/drm_client.c
index d9a2e3695525..dbd73fe8d987 100644
--- a/drivers/gpu/drm/drm_client.c
+++ b/drivers/gpu/drm/drm_client.c

@@ -112,6 +112,43 @@ int drm_client_init(struct drm_device *dev, struct drm_client_dev *client,
 }
 EXPORT_SYMBOL(drm_client_init);

+/**
+ * drm_client_init_from_id - Initialise a DRM client
+ * @minor_id: DRM minor id
+ * @client: DRM client
+ * @name: Client name
+ * @funcs: DRM client functions (optional)
+ *
+ * This function looks up the drm_device using the minor id and initializes the client.
+ * It also registeres the client to avoid a possible race with DRM device unregister.

I think another sentence here would be good, explaining that this is for
drivers outside of drm to expose a specific drm driver in some fashion,
and just outright mention your use-case as an example.

I'm also not sure whether lookup-by-minor is the greatest thing for
kernel-internal lookups like this, maybe Greg has some idea?

What alternatives do you see? Parent device name?

I did a scan to see what others are doing, and most have a consumer name
lookup on the struct device (Device Tree or lookup tables):

I think those are all for other purposes. What we want here is that
some interface things binds to something else. I was thinking sysfs
paths to the underlying struct device (i.e. the one in
drm_device->dev) might be neater, since that's more unique. Using
minors we get that entire trouble of having duplicates (and in the
past triplicatres) due to our uapi-flavors. But in sysfs there's only
one underlying device.

Anyway if there's no precedence and Greg doesn't have ideas either
then I guess we can just go with minor ids. It's about as good as
anything else really.
-Daniel

struct reset_control *__reset_control_get(struct device *dev, const char
*id,
                                          int index, bool shared,
                                          bool optional, bool acquired);

struct iio_channel *iio_channel_get(struct device *dev,
                                    const char *consumer_channel);

struct regulator *__must_check regulator_get(struct device *dev,
                                             const char *id);

struct pwm_device *pwm_get(struct device *dev, const char *con_id)

struct gpio_desc *__must_check gpiod_get(struct device *dev,
                                         const char *con_id,
                                         enum gpiod_flags flags);

SPI and I2C use the bus index as lookup:

extern struct i2c_adapter *i2c_get_adapter(int nr);

extern struct spi_controller *spi_busnum_to_master(u16 busnum);


Noralf.

quoted

quoted

+ *
+ * See drm_client_init() and drm_client_register().
+ *
+ * Returns:
+ * Zero on success or negative error code on failure.
+ */
+int drm_client_init_from_id(unsigned int minor_id, struct drm_client_dev *client,
+                        const char *name, const struct drm_client_funcs *funcs)
+{
+    struct drm_minor *minor;
+    int ret;
+
+    minor = drm_minor_acquire(minor_id);
+    if (IS_ERR(minor))
+            return PTR_ERR(minor);
+
+    mutex_lock(&minor->dev->clientlist_mutex);
+    ret = drm_client_init(minor->dev, client, name, funcs);
+    if (!ret)
+            list_add(&client->list, &minor->dev->clientlist);
+    mutex_unlock(&minor->dev->clientlist_mutex);
+
+    drm_minor_release(minor);
+
+    return ret;
+}
+EXPORT_SYMBOL(drm_client_init_from_id);
+
 /**
  * drm_client_register - Register client
  * @client: DRM client

-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch