linux-kernel - Re: [PATCH 3/5] driver core: make struct device

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Date:   Wed, 23 Nov 2022 14:14:31 +0100
From:   Maximilian Luz <luzmaximilian@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org
Cc:     Jens Axboe <axboe@...nel.dk>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <lenb@...nel.org>,
        Stefan Richter <stefanr@...6.in-berlin.de>,
        Wolfram Sang <wsa@...nel.org>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Sean Young <sean@...s.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Hans de Goede <hdegoede@...hat.com>,
        Mark Gross <markgross@...nel.org>,
        Vinod Koul <vkoul@...nel.org>,
        Bard Liao <yung-chuan.liao@...ux.intel.com>,
        Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
        Sanyog Kale <sanyog.r.kale@...el.com>,
        Andreas Noever <andreas.noever@...il.com>,
        Michael Jamet <michael.jamet@...el.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Yehezkel Bernat <YehezkelShB@...il.com>,
        Jiri Slaby <jirislaby@...nel.org>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Chaitanya Kulkarni <kch@...dia.com>,
        Ming Lei <ming.lei@...hat.com>,
        Jilin Yuan <yuanjilin@...rlc.com>,
        Alan Stern <stern@...land.harvard.edu>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ira Weiny <ira.weiny@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Won Chung <wonchung@...gle.com>, alsa-devel@...a-project.org,
        devicetree@...r.kernel.org, linux-acpi@...r.kernel.org,
        linux-block@...r.kernel.org, linux-i2c@...r.kernel.org,
        linux-i3c@...ts.infradead.org, linux-input@...r.kernel.org,
        linux-media@...r.kernel.org, linux-serial@...r.kernel.org,
        linux-usb@...r.kernel.org, linux1394-devel@...ts.sourceforge.net,
        platform-driver-x86@...r.kernel.org
Subject: Re: [PATCH 3/5] driver core: make struct device_type.uevent() take a
 const *

Hi,

On 11/23/22 13:25, Greg Kroah-Hartman wrote:
> The uevent() callback in struct device_type should not be modifying the
> device that is passed into it, so mark it as a const * and propagate the
> function signature changes out into all relevant subsystems that use
> this callback.

[...]

> diff --git a/drivers/platform/surface/aggregator/bus.c b/drivers/platform/surface/aggregator/bus.c
> index de539938896e..407eb55050a6 100644
> --- a/drivers/platform/surface/aggregator/bus.c
> +++ b/drivers/platform/surface/aggregator/bus.c
> @@ -35,9 +35,9 @@ static struct attribute *ssam_device_attrs[] = {
>   };
>   ATTRIBUTE_GROUPS(ssam_device);
>   
> -static int ssam_device_uevent(struct device *dev, struct kobj_uevent_env *env)
> +static int ssam_device_uevent(const struct device *dev, struct kobj_uevent_env *env)
>   {
> -	struct ssam_device *sdev = to_ssam_device(dev);
> +	const struct ssam_device *sdev = to_ssam_device(dev);
>   
>   	return add_uevent_var(env, "MODALIAS=ssam:d%02Xc%02Xt%02Xi%02Xf%02X",
>   			      sdev->uid.domain, sdev->uid.category,

[...]

> --- a/include/linux/surface_aggregator/device.h
> +++ b/include/linux/surface_aggregator/device.h
> @@ -229,7 +229,7 @@ static inline bool is_ssam_device(struct device *d)
>    * Return: Returns a pointer to the &struct ssam_device wrapping the given
>    * device @d.
>    */
> -static inline struct ssam_device *to_ssam_device(struct device *d)
> +static inline struct ssam_device *to_ssam_device(const struct device *d)
>   {
>   	return container_of(d, struct ssam_device, dev);
>   }

I am slightly conflicted about this change as that now more or less
implicitly drops the const. So I'm wondering if it wouldn't be better to
either create a function specifically for const pointers or to just
open-code it in the instance above.

I guess we could also convert this to a macro. Then at least there
wouldn't be an explicit and potentially misleading const-conversion
indicated in the function signature.

Regards,
Max