linux-kernel - Re: [PATCH] regmap-i2c: add 16 bits register width support

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Date:   Thu, 23 Apr 2020 15:45:29 +0100
From:   Mark Brown <broonie@...nel.org>
To:     AceLan Kao <acelan.kao@...onical.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Aaron Sierra <asierra@...-inc.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] regmap-i2c: add 16 bits register width support

On Thu, Apr 23, 2020 at 04:58:57PM +0800, AceLan Kao wrote:
> This allows to access data with 16 bits register width
> via i2c smbus block functions.

> The implementation is inspired by below commit
> https://patchwork.ozlabs.org/patch/545292/

Do you actually have a system that needs this or is it just being
implemented for completeness?  The patch you link to mentions that there
are correctness issues with this implementation.

Please include human readable descriptions of things like commits and
issues being discussed in e-mail in your mails, this makes them much
easier for humans to read especially when they have no internet access.
I do frequently catch up on my mail on flights or while otherwise
travelling so this is even more pressing for me than just being about
making things a bit easier to read.

> @@ -255,6 +312,10 @@ static const struct regmap_bus *regmap_get_i2c_bus(struct i2c_client *i2c,
>  		 i2c_check_functionality(i2c->adapter,
>  					 I2C_FUNC_SMBUS_I2C_BLOCK))
>  		return &regmap_i2c_smbus_i2c_block;
> +	else if (config->val_bits == 8 && config->reg_bits == 16 &&
> +		i2c_check_functionality(i2c->adapter,
> +					I2C_FUNC_SMBUS_I2C_BLOCK))
> +		return &regmap_i2c_smbus_i2c_block_reg16;

OTOH we'll only use it if the device wouldn't otherwise work so I'm not
sure that it's any worse than just hoping the bus is uncontested,
hopefully system designers have taken this into account when building
systems without real I2C controllers.

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