linux-kernel - Re: Implementation of fwnode_operations :: device_get_match

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Date:   Mon, 27 Feb 2023 14:18:59 +0200
From:   Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To:     Vladimir Oltean <vladimir.oltean@....com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Daniel Scally <djrscally@...il.com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Implementation of fwnode_operations :: device_get_match_data()
 for software nodes?

Hi Vladimir,

On Thu, Feb 23, 2023 at 10:37:13PM +0200, Vladimir Oltean wrote:
> Hi,
> 
> I have a need to instantiate a driver written for OF which calls
> device_get_match_data(dev) to get various information based on the
> compatible string.
> 
> I am creating a software node based on the following properties:
> 
> 	struct property_entry props[2] = {
> 		PROPERTY_ENTRY_STRING("compatible", compatible),
> 		{},
> 	};
> 
> (I see I'm not the only one doing this, some drivers/platform/x86/x86-android-tablets.c
> and drivers/platform/chrome/chromeos_laptop.c also do it)
> 
> and the driver in question does begin to probe, but its match_data is
> NULL, because the operation from the title isn't implemented for
> software nodes. So probing ultimately fails.
> 
> Is there some sort or reason why this doesn't exist, other than a lack
> of need?

There has not been any need for it before.

> Can someone please help me with an implementation of this feature?

Try this - I'm sorry, I don't know does it actually work:

diff --git a/drivers/base/swnode.c b/drivers/base/swnode.c
index 1886995a0b3a3..5262b49c7c790 100644
--- a/drivers/base/swnode.c
+++ b/drivers/base/swnode.c
@@ -9,6 +9,7 @@
 #include <linux/device.h>
 #include <linux/kernel.h>
 #include <linux/property.h>
+#include <linux/mod_devicetable.h>
 #include <linux/slab.h>
 
 #include "base.h"
@@ -379,6 +380,25 @@ static void software_node_put(struct fwnode_handle *fwnode)
        kobject_put(&swnode->kobj);
 }
 
+static const void *
+software_node_get_match_data(const struct fwnode_handle *fwnode, const struct device *dev)
+{
+       const struct of_device_id *id;
+       const char *compat;
+
+       if (!dev->driver || !dev->driver->of_match_table)
+               return NULL;
+
+       if (fwnode_property_read_string(fwnode, "compatible", &compat))
+               return NULL;
+
+       for (id = dev->driver->of_match_table; id->compatible[0]; id++)
+               if (!strcmp(compat, id->compatible))
+                       return id->data;
+
+       return NULL;
+}
+
 static bool software_node_property_present(const struct fwnode_handle *fwnode,
                                           const char *propname)
 {
@@ -662,6 +682,7 @@ software_node_graph_parse_endpoint(const struct fwnode_handle *fwnode,
 static const struct fwnode_operations software_node_ops = {
        .get = software_node_get,
        .put = software_node_put,
+       .device_get_match_data = software_node_get_match_data,
        .property_present = software_node_property_present,
        .property_read_int_array = software_node_read_int_array,
        .property_read_string_array = software_node_read_string_array,

-- 
heikki