Re: [PATCH 01/12 v2] Platform: add a dev_groups pointer to struct platform_driver

[Dmitry Torokhov <dmitry.torokhov@gmail.com>]

On Fri, Jul 19, 2019 at 08:52:20PM +0900, Greg Kroah-Hartman wrote:
> On Sat, Jul 06, 2019 at 10:39:38AM -0700, Dmitry Torokhov wrote:
> > On Sat, Jul 6, 2019 at 10:19 AM Greg Kroah-Hartman
> > <gregkh@linuxfoundation.org> wrote:
> > >
> > > On Sat, Jul 06, 2019 at 10:04:39AM -0700, Dmitry Torokhov wrote:
> > > > Hi Greg,
> > > >
> > > > On Sat, Jul 6, 2019 at 1:32 AM Greg Kroah-Hartman
> > > > <gregkh@linuxfoundation.org> wrote:
> > > > >
> > > > > On Thu, Jul 04, 2019 at 02:17:22PM -0700, Dmitry Torokhov wrote:
> > > > > > Hi Greg,
> > > > > >
> > > > > > On Thu, Jul 4, 2019 at 5:15 AM Greg Kroah-Hartman
> > > > > > <gregkh@linuxfoundation.org> wrote:
> > > > > > >
> > > > > > > Platform drivers like to add sysfs groups to their device, but right now
> > > > > > > they have to do it "by hand".  The driver core should handle this for
> > > > > > > them, but there is no way to get to the bus-default attribute groups as
> > > > > > > all platform devices are "special and unique" one-off drivers/devices.
> > > > > > >
> > > > > > > To combat this, add a dev_groups pointer to platform_driver which allows
> > > > > > > a platform driver to set up a list of default attributes that will be
> > > > > > > properly created and removed by the platform driver core when a probe()
> > > > > > > function is successful and removed right before the device is unbound.
> > > > > >
> > > > > > Why is this limited to platform bus? Drivers for other buses also
> > > > > > often want to augment list of their attributes during probe(). I'd
> > > > > > move it to generic probe handling.
> > > > >
> > > > > This is not limited to the platform at all, the driver core supports
> > > > > this for any bus type today, but it's then up to the bus-specific code
> > > > > to pass that on to the driver core.  That's usually set for the
> > > > > bus-specific attributes that they want exposed for all devices of that
> > > > > bus type (see the bus_groups, dev_groups, and drv_groups pointers in
> > > > > struct bus_type).
> > > > >
> > > > > For the platform devices, the problem is that this is something that the
> > > > > individual drivers want after they bind to the device.  And as all
> > > > > platform devices are "different" they can't be a "common" set of
> > > > > attributes, so they need to be created after the device is bound to the
> > > > > driver.
> > > >
> > > > I believe that your assertion that only platform devices want to
> > > > install custom attributes is incorrect.
> > >
> > > Sorry, I didn't mean to imply that only platform drivers want to do
> > > this, as you say, many other drivers do as well.
> > >
> > > > Drivers for devices attached
> > > > to serio, i2c, USB, spi, etc, etc, all have additional attributes:
> > > >
> > > > dtor@dtor-ws:~/kernel/work (master *)$ grep -l '\(i2c\|usb\|spi\)'
> > > > `git grep -l '\(device_add_group\|sysfs_create_group\)' -- drivers` |
> > > > wc -l
> > > > 170
> > > >
> > > > I am pretty sure some of this count is false positives, but majority
> > > > is actually proper hits.
> > >
> > > Yeah, I know, we need to add this type of functionality to those busses
> > > as well.  I don't see a way of doing it other than this bus-by-bus
> > > conversion, do you?
> > 
> > Can't you push the **dev_groups from platform driver down to the
> > generic driver structure and handle them in driver_sysfs_add()?
> 
> Sorry for the delay, got busy with the merge window...
> 
> Anyway, no, we can't call this then, because driver_sysfs_add() is
> called before probe() is called.  So if probe() fails, we don't bind the
> device to the driver.  We also should not be creating sysfs files for a
> driver that has not had probe() called yet, as internal structures will
> not be set up at that time.

Ah, yes, I got confused by the fact that driver_sysfs_remove is called
early. Anyway, I think you want something like this:

diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index 0df9b4461766..61d9d650d890 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -515,9 +515,17 @@ static int really_probe(struct device *dev, struct device_driver *drv)
 			goto probe_failed;
 	}
 
+	if (device_add_groups(dev, drv->dev_groups)) {
+		printk(KERN_ERR "%s: device_add_groups(%s) failed\n",
+			__func__, dev_name(dev));
+		goto dev_groups_failed;
+	}
+
 	if (test_remove) {
 		test_remove = false;
 
+		device_remove_groups(dev, drv->dev_groups);
+
 		if (dev->bus->remove)
 			dev->bus->remove(dev);
 		else if (drv->remove)
@@ -545,6 +553,11 @@ static int really_probe(struct device *dev, struct device_driver *drv)
 		 drv->bus->name, __func__, dev_name(dev), drv->name);
 	goto done;
 
+dev_groups_failed:
+	if (dev->bus->remove)
+		dev->bus->remove(dev);
+	else if (drv->remove)
+		drv->remove(dev);
 probe_failed:
 	if (dev->bus)
 		blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
@@ -1075,6 +1088,8 @@ static void __device_release_driver(struct device *dev, struct device *parent)
 
 		pm_runtime_put_sync(dev);
 
+		device_remove_groups(dev, drv->dev_groups);
+
 		if (dev->bus && dev->bus->remove)
 			dev->bus->remove(dev);
 		else if (drv->remove)
diff --git a/include/linux/device.h b/include/linux/device.h
index 4a295e324ac5..12aa8c687404 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -259,6 +259,8 @@ enum probe_type {
  * @resume:	Called to bring a device from sleep mode.
  * @groups:	Default attributes that get created by the driver core
  *		automatically.
+ * @dev_groups:	Additional attributes attached to device instance once the
+ *		it is bound to the driver.
  * @pm:		Power management operations of the device which matched
  *		this driver.
  * @coredump:	Called when sysfs entry is written to. The device driver
@@ -293,6 +295,7 @@ struct device_driver {
 	int (*suspend) (struct device *dev, pm_message_t state);
 	int (*resume) (struct device *dev);
 	const struct attribute_group **groups;
+	const struct attribute_group **dev_groups;
 
 	const struct dev_pm_ops *pm;
 	void (*coredump) (struct device *dev);


Thanks.

-- 
Dmitry