linux-kernel - Re: [PATCH v11 5/8] i2c: fsi: Add transfer implementation

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Message-ID: <f3085f807e19d9c5d36ef9cded2b3ee59e560899.camel@kernel.crashing.org>
Date:   Wed, 11 Jul 2018 09:39:15 +1000
From:   Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:     Eddie James <eajames@...ux.vnet.ibm.com>,
        Wolfram Sang <wsa@...-dreams.de>
Cc:     linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, robh+dt@...nel.org, joel@....id.au,
        mark.rutland@....com, gregkh@...uxfoundation.org,
        rdunlap@...radead.org, andy.shevchenko@...il.com, peda@...ntia.se
Subject: Re: [PATCH v11 5/8] i2c: fsi: Add transfer implementation

On Tue, 2018-07-10 at 12:52 -0500, Eddie James wrote:
> 
> On 07/09/2018 05:41 PM, Wolfram Sang wrote:
> > > +	cmd |= FIELD_PREP(I2C_CMD_ADDR, msg->addr >> 1);
> > 
> > I just noticed this and wonder: Don't you need the LSB of the address?
> > It is not the RW flag, this is encoded in msg->flags.
> 
> So, the hardware interprets the LSB as the RW flag. It wouldn't be 
> possible to have a device addressed with the LSB set on this I2C master.

What do you mean ? That doesn't sound right... 
> 
> > 
> > Also, no seperate handling for 10 bit addresses? Technically, 7-bit 0x50
> > is different on the wire from 10-bit 0x050. This is minor, though. There
> > are no 10-bit devices out there. Still, did you test 10-bit support?
> 
> Indeed, real 10-bit addresses require some additional manipulation of 
> this I2C master in order to work. We don't support it right now.
> 
> Thanks,
> Eddie
> 
> > 
> > Rest looks good.
> >