linux-kernel - Re: [RFC PATCH v2 6/6] driver core: add compatible string in sysfs for platform devices

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Date:   Wed, 17 Aug 2022 17:30:56 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Nipun Gupta <nipun.gupta@....com>
Cc:     robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org,
        rafael@...nel.org, eric.auger@...hat.com,
        alex.williamson@...hat.com, cohuck@...hat.com,
        puneet.gupta@....com, song.bao.hua@...ilicon.com,
        mchehab+huawei@...nel.org, maz@...nel.org, f.fainelli@...il.com,
        jeffrey.l.hugo@...il.com, saravanak@...gle.com,
        Michael.Srba@...nam.cz, mani@...nel.org, yishaih@...dia.com,
        jgg@...pe.ca, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, kvm@...r.kernel.org, okaya@...nel.org,
        harpreet.anand@....com, nikhil.agarwal@....com,
        michal.simek@....com, git@....com
Subject: Re: [RFC PATCH v2 6/6] driver core: add compatible string in sysfs
 for platform devices

On Wed, Aug 17, 2022 at 08:35:42PM +0530, Nipun Gupta wrote:
> This change adds compatible string for the platform based
> devices.

What exactly is a "compatible string"?

> 
> Signed-off-by: Nipun Gupta <nipun.gupta@....com>
> ---
>  Documentation/ABI/testing/sysfs-bus-platform |  8 +++++++
>  drivers/base/platform.c                      | 23 ++++++++++++++++++++
>  2 files changed, 31 insertions(+)
> 
> diff --git a/Documentation/ABI/testing/sysfs-bus-platform b/Documentation/ABI/testing/sysfs-bus-platform
> index c4dfe7355c2d..d95ff83d768c 100644
> --- a/Documentation/ABI/testing/sysfs-bus-platform
> +++ b/Documentation/ABI/testing/sysfs-bus-platform
> @@ -54,3 +54,11 @@ Description:
>  		Other platform devices use, instead:
>  
>  			- platform:`driver name`
> +
> +What:		/sys/bus/platform/devices/.../compatible
> +Date:		August 2022
> +Contact:	Nipun Gupta <nipun.gupta@....com>
> +Description:
> +		compatible string associated with the device. This is
> +		a read only and is visible if the device have "compatible"
> +		property associated with it.

Where is it defined what a compatible property is?

> diff --git a/drivers/base/platform.c b/drivers/base/platform.c
> index 51bb2289865c..94c33efaa9b8 100644
> --- a/drivers/base/platform.c
> +++ b/drivers/base/platform.c
> @@ -1289,10 +1289,25 @@ static ssize_t driver_override_store(struct device *dev,
>  }
>  static DEVICE_ATTR_RW(driver_override);
>  
> +static ssize_t compatible_show(struct device *dev, struct device_attribute *attr,
> +			      char *buf)
> +{
> +	const char *compat;
> +	int ret;
> +
> +	ret = device_property_read_string(dev, "compatible", &compat);
> +	if (ret != 0)
> +		return 0;

Shouldn't you return an error here?

thanks,

greg k-h