linux-kernel - Re: [PATCH v5 3/3] gpio: ws16c48: Migrate to the regmap API

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Date:   Mon, 3 Apr 2023 18:20:56 -0400
From:   William Breathitt Gray <william.gray@...aro.org>
To:     Mark Brown <broonie@...nel.org>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <brgl@...ev.pl>,
        linux-kernel@...r.kernel.org, linux-gpio@...r.kernel.org,
        techsupport@...systems.com,
        Paul Demetrotion <pdemetrotion@...systems.com>,
        Michael Walle <michael@...le.cc>
Subject: Re: [PATCH v5 3/3] gpio: ws16c48: Migrate to the regmap API

On Mon, Apr 03, 2023 at 10:12:44PM +0100, Mark Brown wrote:
> On Sun, Apr 02, 2023 at 10:39:02AM -0400, William Breathitt Gray wrote:
> > On Mon, Mar 27, 2023 at 02:26:37PM +0300, Andy Shevchenko wrote:
> > > On Sun, Mar 26, 2023 at 12:25:59PM -0400, William Breathitt Gray wrote:
> 
> > > > +static const struct regmap_config ws16c48_regmap_config = {
> > > > +	.reg_bits = 8,
> > > > +	.reg_stride = 1,
> > > > +	.val_bits = 8,
> > > > +	.io_port = true,
> > > > +	.max_register = 0xA,
> > > > +	.wr_table = &ws16c48_wr_table,
> > > > +	.rd_table = &ws16c48_rd_table,
> > > > +	.volatile_table = &ws16c48_volatile_table,
> > > > +	.cache_type = REGCACHE_FLAT,
> > > > +};
> 
> > > Do we need regmap lock?
> 
> > We make regmap calls within an interrupt context in this driver so I
> > think we need to disable the default regmap mutex locking behavior; I
> > believe the current raw_spin_lock locking in this driver is enough to
> > protect access.
> 
> The above doesn't configure the regmap locking so you'll have a spinlock
> by default (MMIO being a fast bus).

You're right, it'll be a spinlock in this case and not mutex.
Unfortunately, we'll still need to change that to avoid deadlocks on -rt
kernels [0].

William Breathitt Gray

[0] https://lore.kernel.org/all/1466065537-82027-1-git-send-email-mika.westerberg@linux.intel.com/

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