linux-kernel - Re: [PATCH V3] i2c: designware: fix wrong tx/rx fifo for ACPI

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Date:   Tue, 13 Dec 2016 12:19:45 +0200
From:   Mika Westerberg <mika.westerberg@...ux.intel.com>
To:     Joe Perches <joe@...ches.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Tin Huynh <tnhuynh@....com>,
        Jarkko Nikula <jarkko.nikula@...ux.intel.com>,
        Wolfram Sang <wsa@...-dreams.de>, linux-i2c@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
        Loc Ho <lho@....com>, Thang Nguyen <tqnguyen@....com>,
        Phong Vo <pvo@....com>, patches@....com
Subject: Re: [PATCH V3] i2c: designware: fix wrong tx/rx fifo for ACPI

On Mon, Dec 12, 2016 at 11:35:19AM -0800, Joe Perches wrote:
> On Mon, 2016-12-12 at 21:21 +0200, Mika Westerberg wrote:
> > On Mon, Dec 12, 2016 at 09:02:53PM +0200, Andy Shevchenko wrote:
> > > > +	tx_fifo_depth = ((param1 >> 16) & 0xff) + 1;
> > > > +	rx_fifo_depth = ((param1 >> 8)  & 0xff) + 1;
> > > > +	if (!dev->tx_fifo_depth) {
> > > > +		dev->tx_fifo_depth = tx_fifo_depth;
> > > > +		dev->rx_fifo_depth = rx_fifo_depth;
> > > > +	} else if (tx_fifo_depth) {
> > > > +		dev->tx_fifo_depth = min_t(u32, dev->tx_fifo_depth,
> > > > +				tx_fifo_depth);
> > > > +		dev->rx_fifo_depth = min_t(u32, dev->rx_fifo_depth,
> > > > +				rx_fifo_depth);
> > > > +	}
> > > 
> > > So, let's clarify here:
> > > Is it possible to have an IP without parameter block enabled? I mean to
> > > read something arbitrary (or zeroes, or all-ones) from param1.
> > 
> > Yes and it is Intel IP. Haswell IIRC and it returned zeroes.
> 
> The "+ 1"  in the first set of tx_fifo_depth
> makes the "else if" check unnecessary.

Good point. I did not notice that change at all.

The designware I2C databook I have here says that 0 is reserved value
and FIFO sizes start from 2 so the above is wrong either way.