Re: [PATCH v10 5/7] i2c: fsi: Add transfer implementation

From: Eddie James <eajames@linux.vnet.ibm.com>
To: Wolfram Sang <wsa@the-dreams.de>
Cc: linux-i2c@vger.kernel.org, linux-kernel@vger.kernel.org,
	devicetree@vger.kernel.org, robh+dt@kernel.org,
	benh@kernel.crashing.org, joel@jms.id.au, mark.rutland@arm.com,
	gregkh@linuxfoundation.org, rdunlap@infradead.org,
	andy.shevchenko@gmail.com, peda@axentia.se
Subject: Re: [PATCH v10 5/7] i2c: fsi: Add transfer implementation
Date: Thu, 5 Jul 2018 13:52:13 -0500	[thread overview]
Message-ID: <ab5a5b9c-931e-e8ca-d064-92a917e00a3b@linux.vnet.ibm.com> (raw)
In-Reply-To: <20180702182434.5wxxszpgpf6wergl@ninjato>

On 07/02/2018 01:24 PM, Wolfram Sang wrote:
>>>> +	if (msg->flags & I2C_M_RD)
>>>> +		cmd |= I2C_CMD_READ;
>>> Since you support MANGLING, I'd think you can easily support
>>> I2C_M_REV_DIR_ADDR here, too?
>> Hm, I don't really understand the purpose of that flag. From the docs:
>>
>> This toggles the Rd/Wr flag. That is, if you want to do a write, but
>>      need to emit an Rd instead of a Wr, or vice versa, you set this
>>      flag. For example:
>> S Addr Rd [A] Data [A] Data [A] ... [A] Data [A] P
>>
>> I don't think our hardware supports this type of operation.
> I'd think something like this should do:
>
> 	if (msg->flags & I2C_M_REV_DIR_ADDR)
> 		cmd ^= I2C_CMD_READ;

I meant that the hardware cannot interpret this, it would be a 
meaningless command unfortunately.

>