From: lars@metafoo.de (Lars-Peter Clausen)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH 3/4] devicetree: bindings: Add defeature-repeated-start property for Cadence I2C
Date: Tue, 02 Dec 2014 16:12:48 +0100 [thread overview]
Message-ID: <547DD6F0.6060006@metafoo.de> (raw)
In-Reply-To: <20141202141548.GA5883@katana>
On 12/02/2014 03:15 PM, Wolfram Sang wrote:
>>> What do you do when disable repeated start? Sending STOP and START? If
>>> so, this is really something different than repeated start. By using
>>> I2C_FUNC_I2C a user expects repeated start, so if the HW does not
>>> support it, we should say so and don't try to emulate it with something
>>> different.
>>
>> Yes, we send stop.
>
> As said before, this is wrong. Another master could interfere between
> the messages when using stop+start. This is no replacement for repeated
> start.
More importantly a lot of I2C slaves also reset their internal state machine
on a stop. So e.g. if reading a register is implemented by doing
start,write,repeated start,read,stop and you replace that with
start,write,stop,start,read,stop you'll always read register zero instead of
the register you wanted to read.
- Lars
next prev parent reply other threads:[~2014-12-02 15:12 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-12-02 10:05 [PATCH 0/4] Cadence I2C driver fixes Harini Katakam
2014-12-02 10:05 ` [PATCH 1/4] i2c: cadence: Handle > 252 byte transfers Harini Katakam
2014-12-02 10:05 ` [PATCH 2/4] i2c: cadence: Set the hardware time-out register to maximum value Harini Katakam
2014-12-03 11:28 ` Wolfram Sang
2014-12-02 10:05 ` [PATCH 3/4] devicetree: bindings: Add defeature-repeated-start property for Cadence I2C Harini Katakam
2014-12-02 11:19 ` Mark Rutland
2014-12-02 12:13 ` Harini Katakam
2014-12-02 12:52 ` Wolfram Sang
2014-12-02 13:10 ` Harini Katakam
2014-12-02 13:16 ` Wolfram Sang
2014-12-02 13:30 ` Harini Katakam
2014-12-02 14:15 ` Wolfram Sang
2014-12-02 15:12 ` Lars-Peter Clausen [this message]
2014-12-02 10:05 ` [PATCH 4/4] i2c: cadence: Defeature repeated start based on devicetree property Harini Katakam
2014-12-02 11:21 ` Mark Rutland
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