On Sun, Sep 26, 2021 at 04:15:42PM +0100, Jonathan Cameron wrote:

On Mon, 20 Sep 2021 19:09:13 +0900
William Breathitt Gray [off-list ref] wrote:

quoted

On Sun, Sep 12, 2021 at 05:18:42PM +0100, Jonathan Cameron wrote:

quoted

On Fri, 27 Aug 2021 12:47:51 +0900
William Breathitt Gray [off-list ref] wrote:
  

quoted

This patch introduces a character device interface for the Counter
subsystem. Device data is exposed through standard character device read
operations. Device data is gathered when a Counter event is pushed by
the respective Counter device driver. Configuration is handled via ioctl
operations on the respective Counter character device node.

Cc: David Lechner <david@lechnology.com>
Cc: Gwendal Grignou <redacted>
Cc: Dan Carpenter <redacted>
Cc: Oleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: William Breathitt Gray <redacted>  

Hi William,

Why the bit based lock?  It feels like a mutex_trylock() type approach or
spinlock_trylock() would be a more common solution to this problem.
There is precedence for doing what you have here though so I'm not that
worried about it.  

Hi Jonathan,

We originally used a mutex for this, but Jarkko discovered that this
produced a warning because chrdev_lock would be held when returning to
user space:
https://lore.kernel.org/linux-arm-kernel/YOq19zTsOzKA8v7c@shinobu/T/#m6072133d418d598a5f368bb942c945e46cfab9a5 (local)

Following David Lechner's suggestion, I decided to reimplement
chrdev_lock as a bitmap using an atomic flag.

Ok.  I'm not sure bit lock was quite what was intended (as there is only one of them)
but I suppose it doesn't greatly matter.

It didn't cross my mind before, but would declaring chrdev_lock as an
atomic_t be a more appropriate solution here because we have only one
flag?

William Breathitt Gray