Re: [PATCH 00/12] iio: add new backend framework

[Nuno Sá]

On Thu, 2023-11-23 at 18:36 +0100, Olivier MOYSAN wrote:
> Hi Nuno,
> 
> On 11/21/23 11:20, Nuno Sa via B4 Relay wrote:
> > Hi all,
> > 
> > This is a Framework to handle complex IIO aggregate devices.
> > 
> > The typical architecture is to have one device as the frontend device which
> > can be "linked" against one or multiple backend devices. All the IIO and
> > userspace interface is expected to be registers/managed by the frontend
> > device which will callback into the backends when needed (to get/set
> > some configuration that it does not directly control).
> > 
> > The basic framework interface is pretty simple:
> >   - Backends should register themselves with @devm_iio_backend_register()
> >   - Frontend devices should get backends with @devm_iio_backend_get()
> > 
> > (typical provider - consumer stuff)
> > 
> > This is the result of the discussions in [1] and [2]. In short, both ADI
> > and STM wanted some way to control/get configurations from a kind of
> > IIO aggregate device. So discussions were made to have something that
> > serves and can be used by everyone.
> > 
> > The main differences with the converter framework RFC [1]:
> > 
> > 1) Dropped the component framework. One can get more overview about
> > the concerns on the references but the main reasons were:
> >   * Relying on providing .remove() callbacks to be allowed to use device
> >     managed functions. I was not even totally sure about the correctness
> >     of it and in times where everyone tries to avoid that driver
> >     callback, it could lead to some maintenance burden.
> >   * Scalability issues. As mentioned in [2], to support backends defined
> >     in FW child nodes was not so straightforward with the component
> >     framework.
> >   * Device links can already do some of the things that made me
> >     try the component framework (eg: removing consumers on suppliers
> >     unbind).
> > 
> > 2) Only support the minimal set of functionality to have the devices in
> >     the same state as before using the backend framework. New features
> >     will be added afterwards.
> > 
> > 3) Moved the API docs into the .c files.
> > 
> > 4) Moved the framework to the IIO top dir and renamed it to
> >     industrialio-backend.c.
> > 
> > Also, as compared with the RFC in [2], I don't think there are that many
> > similarities other than the filename. However, it should now be pretty
> > straight for Olivier to build on top of it. Also to mention that I did
> > grabbed patch 1 ("of: property: add device link support for
> > io-backends") from that series and just did some minor changes:
> > 
> 
> I did not already look at the framework patches in detail, but at first 
> glance it looks fine.
> 
> I confirm that it has been quite straightforward to build on top of this 
> framework, as it remains close to my first approach. I had only some 
> small changes to do, to match the API, and to get it alive. This is great.
> 
> I see just one concern regarding ADC generic channel bindings support.
> Here we have no devices associated to the channel sub-nodes. So, I 
> cannot figure out we could use the devm_iio_backend_get() API, when 
> looking for backend handle in channels sub-nodes. I have to think about it.
> 

Yeah, I'm keeping the series small (as Jonathan asked in the RFC) and just with basic
stuff needed to get the ad9647 driver in the exact same state as before the
framework. So yes, it's the same deal as with the component approach. You'll need to
add support for it. But, in this case, I believe it should be as straight as:

-/**
- * devm_iio_backend_get - Get a backend device
- * @dev:       Device where to look for the backend.
- * @name:      Backend name.
- *
- * Get's the backend associated with @dev.
- *
- * RETURNS:
- * A backend pointer, negative error pointer otherwise.
- */
-struct iio_backend *devm_iio_backend_get(struct device *dev, const char *name)
+struct iio_backend *devm_fwnode_iio_backend_get(struct device *dev,
+                                               const struct fwnode_handle *fwnode,
+                                               const char *name)
 {
-       struct fwnode_handle *fwnode;
+       struct fwnode_handle *back_fwnode;
        struct iio_backend *back;
        int index = 0, ret;

@@ -195,20 +187,20 @@ struct iio_backend *devm_iio_backend_get(struct device *dev,
const char *name)
                        return ERR_PTR(index);
        }

-       fwnode = fwnode_find_reference(dev_fwnode(dev), "io-backends", index);
-       if (IS_ERR(fwnode)) {
+       back_fwnode = fwnode_find_reference(fwnode, "io-backends", index);
+       if (IS_ERR(back_fwnode)) {
                dev_err(dev, "Cannot get Firmware reference\n");
-               return ERR_CAST(fwnode);
+               return ERR_CAST(back_fwnode);
        }

        guard(mutex)(&iio_back_lock);
        list_for_each_entry(back, &iio_back_list, entry) {
                struct device_link *link;

-               if (!device_match_fwnode(back->dev, fwnode))
+               if (!device_match_fwnode(back->dev, back_fwnode))
                        continue;

-               fwnode_handle_put(fwnode);
+               fwnode_handle_put(back_fwnode);
                kref_get(&back->ref);
                if (!try_module_get(back->owner)) {
                        dev_err(dev, "Cannot get module reference\n");
@@ -229,9 +221,25 @@ struct iio_backend *devm_iio_backend_get(struct device *dev,
const char *name)
                return back;
        }

-       fwnode_handle_put(fwnode);
+       fwnode_handle_put(back_fwnode);
        return ERR_PTR(-EPROBE_DEFER);
 }
+EXPORT_SYMBOL_GPL(devm_fwnode_iio_backend_get);
+
+/**
+ * devm_iio_backend_get - Get a backend device
+ * @dev:       Device where to look for the backend.
+ * @name:      Backend name.
+ *
+ * Get's the backend associated with @dev.
+ *
+ * RETURNS:
+ * A backend pointer, negative error pointer otherwise.
+ */
+struct iio_backend *devm_iio_backend_get(struct device *dev, const char *name)
+{
+       return devm_fwnode_iio_backend_get(dev, dev_fwnode(dev), name);
+}
 EXPORT_SYMBOL_GPL(devm_iio_backend_get);

 /**

Completely untested (not even compiled :)). Anyways, the goal is to just have the
minimum accepted and you can then send the needed patches for subnode lookups.


> > 1) Renamed the property from "io-backend" to "io-backends".
> > 2) No '#io-backend-cells' as it's not supported/needed by the framework
> > (at least for now) .
> > 
> > Regarding the driver core patch
> > ("driver: core: allow modifying device_links flags"), it is more like a
> > RFC one. I'm not really sure if the current behavior isn't just
> > expected/wanted. Since I could not really understand if it is or not
> > (or why the different handling DL_FLAG_AUTOREMOVE_CONSUMER vs
> > DL_FLAG_AUTOREMOVE_SUPPLIER), I'm sending out the patch.
> > 
> > Jonathan,
> > 
> > I also have some fixes and cleanups for the ad9467 driver. I added
> > Fixes tags but I'm not sure if it's really worth it to backport them (given
> > what we already discussed about these drivers). I'll leave that to you
> > :).
> > 
> > I'm also not sure if I'm missing some tags (even though the series
> > is frankly different from [2]).
> > 
> > Olivier,
> > 
> > If you want to be included as a Reviewer let me know and I'll happily do
> > so in the next version.
> > 
> 
> Yes, please add me as reviewer.
> Thanks.
> Olivier

Will do.

- Nuno Sá
>