Hi Tony,
On Mon, Aug 20, 2018 at 07:55:22AM -0700, Tony Lindgren wrote:
> * Stefan Lengfeld <contact@xxxxxxxxxxxxxxx> [180813 21:19]:
> > Using i2c_transfer() to set the shutdown bit is more reliable than using
> > regmap. Furthermore you have to void the default lock configuration in
> > the regmap configuration, e.g. by setting use_hwlock to true, to used in
> > atomic/IRQ disabled contexts.
>
> Hmm so this is a bit worrying, does this mean that regmap can't deal
> with atomic i2c then?
In theory yes. Regmap can support IRQ/sleep less operation, but you have
to ensure that the whole callstack trough the regmap interface and code
never calls sleep or waits for a lock.
First you have to use a sleep-less lock/unlock implementation in the
regmap_config e.g.
static struct regmap_config da9062_regmap_config = {
[...]
/* Enable hwclock to use a sleep-free lock implementation */
.use_hwlock = 1,
Or providing an own implementations of the regmap callbacks
struct regmap_config {
[...]
regmap_lock lock;
regmap_unlock unlock;
If have tried that and tested the code with
CONFIG_DEBUG_ATOMIC_SLEEP
But I have still seen a sleep violation in the regmap cache
implementation. Somewhere a cache handler was acquiring a lock or made a
memory allocation. At that point I gave up and just called the I²C
interface directly.
So I would say, regmap can support atomic I²C transfers, but you need a
lot of tweaking and on device testing.
Kind regards,
Stefan
