linux-kernel - Re: [PATCH 1/2] drivers: base: swnode: link devices to software nodes

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Message-ID: <e36fb47b-2969-5f53-97d4-8e94b4c98283@intel.com>
Date:   Tue, 30 Jul 2019 16:49:50 +0200
From:   "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
To:     Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Linus Walleij <linus.walleij@...aro.org>
Cc:     Dmitry Torokhov <dmitry.torokhov@...il.com>,
        "Enrico Weigelt, metux IT consult" <info@...ux.net>,
        linux-input@...r.kernel.org, linux-gpio@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Andy Shevchenko <andy.shevchenko@...il.com>
Subject: Re: [PATCH 1/2] drivers: base: swnode: link devices to software nodes

On 7/30/2019 1:52 PM, Heikki Krogerus wrote:
> On Mon, Jul 29, 2019 at 03:15:32PM +0200, Dmitry Torokhov wrote:
>> On Mon, Jul 29, 2019 at 03:07:15PM +0300, Heikki Krogerus wrote:
>>> On Sat, Jul 13, 2019 at 12:52:58AM -0700, Dmitry Torokhov wrote:
>>>> It is helpful to know what device, if any, a software node is tied to, so
>>>> let's store a pointer to the device in software node structure. Note that
>>>> children software nodes will inherit their parent's device pointer, so we
>>>> do not have to traverse hierarchy to see what device the [sub]tree belongs
>>>> to.
>>>>
>>>> We will be using the device pointer to locate GPIO lookup tables for
>>>> devices with static properties.
>>>>
>>>> Signed-off-by: Dmitry Torokhov <dmitry.torokhov@...il.com>
>>>> ---
>>>>   drivers/base/property.c  |  1 +
>>>>   drivers/base/swnode.c    | 35 ++++++++++++++++++++++++++++++++++-
>>>>   include/linux/property.h |  5 +++++
>>>>   3 files changed, 40 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/base/property.c b/drivers/base/property.c
>>>> index 348b37e64944..3bc93d4b35c4 100644
>>>> --- a/drivers/base/property.c
>>>> +++ b/drivers/base/property.c
>>>> @@ -527,6 +527,7 @@ int device_add_properties(struct device *dev,
>>>>   	if (IS_ERR(fwnode))
>>>>   		return PTR_ERR(fwnode);
>>>>   
>>>> +	software_node_link_device(fwnode, dev);
>>>>   	set_secondary_fwnode(dev, fwnode);
>>>>   	return 0;
>>>>   }
>>>> diff --git a/drivers/base/swnode.c b/drivers/base/swnode.c
>>>> index 7fc5a18e02ad..fd12eea539b6 100644
>>>> --- a/drivers/base/swnode.c
>>>> +++ b/drivers/base/swnode.c
>>>> @@ -24,6 +24,9 @@ struct software_node {
>>>>   
>>>>   	/* properties */
>>>>   	const struct property_entry *properties;
>>>> +
>>>> +	/* device this node is associated with */
>>>> +	struct device *dev;
>>>>   };
>>> Let's not do that! The nodes can be, and in many cases are, associated
>>> with multiple devices.
>> They do? Where? I see that set of properties can be shared between
>> several devices, but when we instantiate SW node we create a new
>> instance for device. This is also how ACPI and OF properties work; they
>> not shared between devices (or, rather, the kernel creates distinct _and
>> single_ devices for instance of ACPI or OF node). I do not think we want
>> swnodes work differently from the other firmware nodes.
> Having multiple devices linked to a single node is quite normal. Most
> multifunctional devices will share a single node. The USB port devices
> will share their node (if they have one) with any device that is
> attached to them. Etc.
>
> If you want to check how this works with ACPI, then find
> "physical_node" named files from sysfs. The ACPI node folders in sysfs
> have symlinks named "physical_node<n>" for every device they are bind
> to. The first one is named just "physical_node", the second
> "physical_node1", the third "physical_node2", and so on.
>
>>> Every device is already linked with the software node kobject, so
>>> isn't it possible to simply walk trough those links in order to check
>>> the devices associated with the node?
>> No, we need to know the exact instance of a device, not a set of
>> devices, because even though some properties can be shared, others can
>> not. For example, even if 2 exactly same touch controllers in the system
>> have "reset-gpios" property, they won't be the same GPIO for the both of
>> them.
> I don't think I completely understand the use case you had in mind for
> this API, but since you planned to use it with the GPIO lookup tables,
> I'm going to assume it's not needed after all. Let's replace those
> with the references instead like I proposed in my reply to the 2/2
> patch.
>
> Linking a single device with a node like that is in any case not
> acceptable nor possible.
>
I think I need to withdraw my ACK here at this point.