linux-kernel - Re: [PATCH v7 5/6] i2c: Add Actions Semiconductor Owl family S900 I2C driver

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Date:   Wed, 1 Aug 2018 10:26:39 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     Wolfram Sang <wsa@...-dreams.de>
Cc:     robh+dt@...nel.org, afaerber@...e.de, linus.walleij@...aro.org,
        linux-i2c@...r.kernel.org, liuwei@...ions-semi.com,
        mp-cs@...ions-semi.com, 96boards@...obotics.com,
        devicetree@...r.kernel.org, andy.shevchenko@...il.com,
        daniel.thompson@...aro.org, amit.kucheria@...aro.org,
        linux-arm-kernel@...ts.infradead.org, linux-gpio@...r.kernel.org,
        linux-kernel@...r.kernel.org, hzhang@...obotics.com,
        bdong@...obotics.com, manivannanece23@...il.com,
        thomas.liau@...ions-semi.com, jeff.chen@...ions-semi.com
Subject: Re: [PATCH v7 5/6] i2c: Add Actions Semiconductor Owl family S900
 I2C driver

Hi Wolfram,

On Tue, Jul 31, 2018 at 10:09:32PM +0200, Wolfram Sang wrote:
> Hi Manivannan,
> 
> On Thu, Jul 26, 2018 at 09:16:02PM +0530, Manivannan Sadhasivam wrote:
> > Add Actions Semiconductor Owl family S900 I2C driver.
> > 
> > Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> > Acked-by: Peter Rosin <peda@...ntia.se>
> 
> Looks mostly good already. Thanks Peter for the initial review!
> 

Thanks to Andy also :)

> > +static irqreturn_t owl_i2c_interrupt(int irq, void *_dev)
> > +{
> > +	struct owl_i2c_dev *i2c_dev = _dev;
> > +	struct i2c_msg *msg = i2c_dev->msg;
> > +	unsigned long flags;
> > +	unsigned int stat, fifostat;
> > +
> > +	spin_lock_irqsave(&i2c_dev->lock, flags);
> > +
> > +	fifostat = readl(i2c_dev->base + OWL_I2C_REG_FIFOSTAT);
> > +	if (fifostat & OWL_I2C_FIFOSTAT_RNB) {
> > +		dev_dbg(&i2c_dev->adap.dev, "received NACK from device\n");
> > +		goto stop;
> > +	}
> > +
> > +	stat = readl(i2c_dev->base + OWL_I2C_REG_STAT);
> > +	if (stat & OWL_I2C_STAT_BEB) {
> > +		dev_dbg(&i2c_dev->adap.dev, "bus error\n");
> > +		goto stop;
> > +	}
> 
> I wonder if you can't pass back the different errors to the upper
> layers? Like -ENXIO for NACK and -EIO for bus error? We have a
> convention for that and it seems your HW can support it. The different
> error codes would then maybe also make the debug outputs obsolete.
> 
> 

Sure, will catch the errors using an i2c_dev member and pass it to upper
layers in owl_i2c_master_xfer.

> > +	/*
> > +	 * Here, -ENXIO will be returned if interrupt occurred but no
> > +	 * read or write happened. Else if msg_ptr equals to message length,
> > +	 * message count will be returned.
> > +	 */
> > +	ret = i2c_dev->msg_ptr == msg->len ? num : -ENXIO;
> 
> I'd think this kinda unusual construct could go then as well by just
> returning the error code derived from the interrupt handler above.
> 

Makes sense! It will become:

ret = i2c_dev->err < 0 ? i2c_dev->err : num;

Thanks,
Mani

> > +static const struct i2c_adapter_quirks owl_i2c_quirks = {
> > +	.flags		= I2C_AQ_COMB | I2C_AQ_COMB_WRITE_FIRST,
> > +	.max_read_len   = 240,
> > +	.max_write_len  = 240,
> > +	.max_comb_1st_msg_len = 6,
> > +	.max_comb_2nd_msg_len = 240,
> > +};
> 
> Yay! Good use of the i2c_adapter_quirks struct :)
> 
> Regards,
> 
>    Wolfram
>