Message-ID: <534D1DDA.40207@free-electrons.com>
Date:	Tue, 15 Apr 2014 13:54:02 +0200
From:	Boris BREZILLON <boris.brezillon@...e-electrons.com>
To:	Mark Brown <broonie@...nel.org>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	Shuge <shuge@...winnertech.com>, kevin@...winnertech.com,
	Chen-Yu Tsai <wens@...e.org>,
	Hans de Goede <hdegoede@...hat.com>,
	Carlo Caione <carlo@...one.org>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	dev@...ux-sunxi.org
Subject: Re: [RFC PATCH v2] regmap: smbus: add support for regmap over SMBus


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On 15/04/2014 12:09, Mark Brown wrote:
> On Tue, Apr 15, 2014 at 09:36:13AM +0200, Boris BREZILLON wrote:
>> On 14/04/2014 23:04, Mark Brown wrote:
>
>>> The transfer type gets set once per device at init time so why not
>>> just parameterise based on val_bytes?
>
>> Actually, you may want to transfer 1 byte registers using the block
>> method (if your device only support block transfers). This depends on
>> the device being accessed and what it supports, but I'm not sure we can
>> assume 1 byte registers will always be transferred using SMBUS byte
>> transfers.
>
> OK, so if this a realistic issue then it seems like it's better to
> implement three different buses - there is not really any common code
> between the various paths.

Okay, I'll create 4 different busses (one for each access type).
BTW, should I keep these implementations in the same source file
(regmap-smbus.c) ?
And, should I keep one method to register an smbus regmap or should I
provide one method per access type and get rid of the
regmap_smbus_transfer_type enum ?

>   This would also mean that you avoid having
> gather write when it can't be implemented.

Correct me if I'm wrong, but they all support gather write.

>
>
> The code is also not validating the lengths for two byte values.

I'm not sure I get this one.
Do you mean I should check that val_size is a 2 byte multiple ?
If this is what you meant, then I should also check it for block transfers.

>
>
>>>> +    case REGMAP_SMBUS_I2C_BLOCK_TRANSFER: +        while (count
>>>>> 0 && !ret) { +            ret =
>>>> i2c_smbus_write_i2c_block_data(ctx->i2c, +
>>>> reg, +                                 ctx->val_bytes, +
>>>> (const u8 *)data);
>
>>> Fix the const correctness of the API rather than casting.
>
>> The API is correct because the i2c_smbus_write_i2c_block does not modify
>> the data pointer.
>> Just removing the const keyword in the cast should be enough, because
>> you can safely cast a non const pointer to a const one.
>
> If you need to cast away from void at all something is going wrong (and
> we appear to be always passing in write buffers as const too, I can't
> remember which operation this was though).

You're right, removing the cast when passing the val argument to the i2c
block transfer functions works.

Best Regards,

Boris

- -- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
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