linux-kernel - Re: [PATCH] i2c: designware: do not disable adapter after transfer

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Date:	Wed, 27 Apr 2016 10:47:11 +0300
From:	Jarkko Nikula <jarkko.nikula@...ux.intel.com>
To:	Lucas De Marchi <lucas.demarchi@...el.com>,
	"linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>
Cc:	"wsa@...-dreams.de" <wsa@...-dreams.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"mika.westerberg@...ux.intel.com" <mika.westerberg@...ux.intel.com>,
	Christian Ruppert <christian.ruppert@...tech.com>
Subject: Re: [PATCH] i2c: designware: do not disable adapter after transfer

On 04/25/2016 06:04 PM, Lucas De Marchi wrote:
>
>
> On 04/25/2016 08:51 AM, Jarkko Nikula wrote:
>
> [ ... ]
>
>>> @@ -413,8 +416,16 @@ static void i2c_dw_xfer_init(struct dw_i2c_dev
>>> *dev)
>>>       struct i2c_msg *msgs = dev->msgs;
>>>       u32 ic_con, ic_tar = 0;
>>>
>>> -    /* Disable the adapter */
>>> -    __i2c_dw_enable(dev, false);
>>> +    if (dev->enabled) {
>>> +        u32 ic_status;
>>> +
>>> +        /* check ic_tar and ic_con can be dynamically updated */
>>> +        ic_status = dw_readl(dev, DW_IC_STATUS);
>>> +        if (ic_status & DW_IC_STATUS_ACTIVITY
>>> +            || !(ic_status & DW_IC_STATUS_TX_EMPTY)) {
>>> +            __i2c_dw_enable(dev, false);
>>> +        }
>>> +    }
>>>
>> Worth to double check this. I see bit 1 means TX FIFO not full and bit 2
>> is TX FIFO completely empty.
>
> the conditions to be able to update IC_TAR dynamically are:
>
>    - Adapter isn't doing any TX/RX operation (IC_STATUS[5] == 0) and
>    - There are no entries in TX FIFO (IC_STATUS[2] == 1)
>
> So... yeah, the condition above seems wrong. I should be reading bit 5,
> not bit 1. Thanks! However:
>
It reads above, bit 2 instead of 1 for TX FIFO checking and then either 
bit 5 or 0 for activity checking.

I'd say it's probably better to check bit 5 instead of bit 0 even bit 0 
is or'ed from bits 5 and 6. I don't know how possible slave support and 
slave being active will play here so it's best to follow spec.

-- 
jarkko