linux-kernel - RE: [PATCH 2/2] i2c: designware: slave should do WRITE_REQUESTED before WRITE

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Date:   Wed, 4 Nov 2020 10:17:29 +0000
From:   <Michael.Wu@...ics.com>
To:     <wsa@...nel.org>
CC:     <jarkko.nikula@...ux.intel.com>,
        <andriy.shevchenko@...ux.intel.com>,
        <mika.westerberg@...ux.intel.com>, <linux-i2c@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <morgan.chang@...ics.com>
Subject: RE: [PATCH 2/2] i2c: designware: slave should do WRITE_REQUESTED
 before WRITE_RECEIVED

Hi Wolfram,

> > dev->status can be used to record the current state, especially Designware
> > I2C controller has no interrupts to identify a write-request. This patch
> 
> Just double-checking: the designware HW does not raise an interrupt when
> its own address + RW bit has been received?

Not exactly. There're an interrupt state name "RD_REQ" but no one named
like "WR_REQ".

For read-request, the slave will get a RD_REQ interrupt. 
For write-request, the slave won't be interrupted until data arrived to
trigger interrupt "RX_FULL".

I tried to use GPIO to simulate an I2C master. I only sent its own
address + W bit without any data and then I got only a STOP_DET interrupt.
If I sent its own address + W bit + one byte data and then I got one
RX_FULL and a STOP_DET.

It seems the controller doesn't interrupt when RW bit is W, but R does.
What do you think, Jarkko?

Sincerely,

Michael Wu