linux-kernel - Re: [PATCHv5 3/3] i2c: altera: Add Altera I2C Controller driver

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Date:   Mon, 31 Jul 2017 22:16:29 +0200
From:   Wolfram Sang <wsa@...-dreams.de>
To:     Thor Thayer <thor.thayer@...ux.intel.com>
Cc:     robh+dt@...nel.org, mark.rutland@....com, davem@...emloft.net,
        gregkh@...uxfoundation.org, mchehab@...nel.org,
        linux-i2c@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCHv5 3/3] i2c: altera: Add Altera I2C Controller driver


> >>+	writel(ALTR_I2C_TFR_CMD_STA | ALTR_I2C_TFR_CMD_STO,
> >>+	       idev->base + ALTR_I2C_TFR_CMD);
> >>+	altr_i2c_reset(idev);
> >
> >Why the second reset?
> >
> 
> I wanted to start from a known clean condition. The first reset would reset
> the hardware. The 2nd would ensure the hardware is ready after clearing the
> bus. Maybe I'm being overly cautious but I don't have a way to check the
> status of the SDA line.

Well, it looks like the function will go for now anyhow...

> >>+		altr_i2c_recover(idev);
> >
> >And no need to reset the bus! Only if SDA is stuck low.
> >
> 
> OK. Unfortunately, we can't check the state of the SDA line so I was being
> extra cautious. I will remove it.

Thanks. Bus recovery really needs a testcase to be checked against.

> >>+static u32 altr_i2c_func(struct i2c_adapter *adap)
> >>+{
> >>+	return I2C_FUNC_I2C;
> >>+}
> >
> >No emulated SMBUS?
> >
> 
> I was focusing on I2C and wasn't sure about SMBus (particularly the minimum
> clock speed). SMBus could be added later but would require some IP changes.

I meant you can add I2C_FUNC_SMBUS_EMUL which makes the I2C core emulate
SMBus-style transactions via I2C messages for you. A lot of drivers
won't work if you don't have this.


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