Re: [PATCH v2 0/4] hwspinlock: add summary in debugfs

[Wolfram Sang <wsa+renesas@sang-engineering.com>]

Hi Matthew,

thank you for your help, that is much appreciated!

On Mon, Jun 29, 2026 at 07:54:41PM +0100, Matthew Wilcox wrote:
> On Mon, Jun 29, 2026 at 10:57:14AM +0200, Wolfram Sang wrote:
> > Okay, seems to work so far. Thank you again! Will merge your patch into
> > my series with your credits. Now I just need to wrap XArray into struct
> > seq_operations. Seems no one has needed that in the kernel so far.
> 
> Huh.  I thought I had done that at some point.  But it was pre-pandemic
> that I was looking at it so maybe I either never did it or I never sent
> it out.

I grepped for all users of 'struct seq_operations' if they used
xarray functionality within a seq-file. No hit, sadly.

I am bit struggling with the initial approach. I would think that I need
to return the current xas with start() and next() from seq_operations.
That would mean dynamic allocating xas with kzalloc. However, xarray
documentation says to put xas on the stack. Can't it be done
dynamically?

> Assuming that we don't want to call pm_runtime_get_sync() under the
> spinlock (and maybe for cleanliness we shouldn't anyway?), I would clear
> the HWSPINLOCK_UNUSED mark in hwspin_lock_request_specific(), drop the
> lock, then if __hwspin_lock_request() fails, set the UNUSED mark again.

Yes, I agree. This is also my fav solution to ensure we can use a
spinlock for the xarray. Hope I can work on it later today.

Happy hacking,

   Wolfram