linux-kernel - Re: [RFC PATCH v1] driver core: Expose device link details in sysfs

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Date:   Mon, 18 May 2020 10:04:35 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Saravana Kannan <saravanak@...gle.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        John Stultz <john.stultz@...aro.org>, kernel-team@...roid.com,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v1] driver core: Expose device link details in sysfs

On Mon, May 18, 2020 at 12:06:07AM -0700, Saravana Kannan wrote:
> It's helpful to be able to look at device link details from sysfs. So,
> expose it in sysfs.
> 
> Say device-A is supplier of device-B. These are the additional files
> this patch would create:
> 
> /sys/class/devlink/device-A:device-B/
> 	flags
> 	supplier/ -> .../device-A/
> 	consumer/ -> .../device-B/
> 
> /sys/devices/.../device-A/
> 	consumer:device-B/ -> /sys/class/devlink/device-A:device-B/
> 
> /sys/devices/.../device-B/
> 	supplier:device-A/ -> /sys/class/devlink/device-A:device-B/
> 
> That way:
> To get a list of all the device link in the system:
> ls /sys/class/devlink/
> 
> To get the consumer names and links of a device:
> ls -d /sys/devices/.../device-X/consumer:*
> 
> To get the supplier names and links of a device:
> ls -d /sys/devices/.../device-X/supplier:*
> 
> For now, I'm just exporting "flags", supplier and consumer for each
> device link. But the goal is to expand it to "state", etc once the
> overall idea is accepted.
> 
> Signed-off-by: Saravana Kannan <saravanak@...gle.com>
> ---
> Greg/Rafael,
> 
> Wanted to check if both of you are okay with the overall idea of
> exporting device link details through sysfs and if using a "struct
> device" is how you'd like to do it. I think this information would be
> helpful in debugging all kinds of suspend/resume, probe and power issues
> in a production system. I didn't want to spend more time on this patch
> before I got your okays.
> 
> I'm not too familiar with the right way to do kobjs and symlinks in
> sysfs -- so apologies any crazy code. But overall, the patch does create
> the layout I describe above and seems to work.

Looks sane to me, nice work.

> I could also remove kref and switch to using link_dev to keep track of
> refcount and releasing stuff, but I wasn't sure if we really needed the
> srcu implementation or not. So didn't remove it in this series and left
> it as is.

I would just leave that alone for now, as that would be a different
change here, right?

thanks,

greg k-h