linux-kernel - Re: [PATCH v2] watchdog: da9062: make restart handler atomic safe

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Message-ID: <20200116072320.f7ia3e76hx7yknqb@porty>
Date:   Thu, 16 Jan 2020 08:23:20 +0100
From:   Stefan Lengfeld <contact@...fanchrist.eu>
To:     Marco Felsch <m.felsch@...gutronix.de>
Cc:     support.opensource@...semi.com, linux@...ck-us.net,
        Adam.Thomson.Opensource@...semi.com,
        linux-watchdog@...r.kernel.org, kernel@...gutronix.de,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] watchdog: da9062: make restart handler atomic safe

Hi Marco,

On Wed, Jan 15, 2020 at 05:23:07PM +0100, Marco Felsch wrote:
> The restart handler is executed during the shutdown phase which is
> atomic/irq-less. The i2c framework supports atomic transfers since
> commit 63b96983a5dd ("i2c: core: introduce callbacks for atomic
> transfers") to address this use case. Using regmap within an atomic
> context is allowed only if the regmap type is MMIO and the cache type
> 'flat' or no cache is used. Using the i2c_smbus_write_byte_data()
> function can be done without additional tests because:
>  1) the DA9062 is an i2c-only device and
>  2) the i2c framework emulates the smbus protocol if the host adapter
>     does not support smbus_xfer by using the master_xfer.
> 
> Signed-off-by: Marco Felsch <m.felsch@...gutronix.de>

Reviewed-by: Stefan Lengfeld <contact@...fanchrist.eu>


On Wed, Marco Flesch wrote [1]:
> I will send a v2 to cover Guenter's suggestion. Can I keep your reviewed
> by tag?

Yes, you can keep it. See above. I also checked by reading the code that
'i2c_smbus_write_byte_data' behaves the same as 'i2c_transfer'. Just
with some indirections.

Kind regards,
    Stefan

[1]: https://www.spinics.net/lists/linux-watchdog/msg17194.html