linux-kernel - Re: [PATCH v4 2/3] i2c: iproc: Add Broadcom iProc I2C Driver

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Date:	Sat, 17 Jan 2015 11:58:33 -0800
From:	Ray Jui <rjui@...adcom.com>
To:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
CC:	Wolfram Sang <wsa@...-dreams.de>, Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	"Ian Campbell" <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Grant Likely <grant.likely@...aro.org>,
	Christian Daudt <bcm@...thebug.org>,
	Matt Porter <mporter@...aro.org>,
	Florian Fainelli <f.fainelli@...il.com>,
	Russell King <linux@....linux.org.uk>,
	"Scott Branden" <sbranden@...adcom.com>,
	<linux-i2c@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<bcm-kernel-feedback-list@...adcom.com>,
	<devicetree@...r.kernel.org>
Subject: Re: [PATCH v4 2/3] i2c: iproc: Add Broadcom iProc I2C Driver



On 1/17/2015 8:01 AM, Uwe Kleine-König wrote:
> Hello,
> 
> On Fri, Jan 16, 2015 at 02:09:28PM -0800, Ray Jui wrote:
>> On 1/15/2015 12:41 AM, Uwe Kleine-König wrote:
>>> On Wed, Jan 14, 2015 at 02:23:32PM -0800, Ray Jui wrote:
>>>> +	 */
>>>> +	val = 1 << M_CMD_START_BUSY_SHIFT;
>>>> +	if (msg->flags & I2C_M_RD) {
>>>> +		val |= (M_CMD_PROTOCOL_BLK_RD << M_CMD_PROTOCOL_SHIFT) |
>>>> +		       (msg->len << M_CMD_RD_CNT_SHIFT);
>>>> +	} else {
>>>> +		val |= (M_CMD_PROTOCOL_BLK_WR << M_CMD_PROTOCOL_SHIFT);
>>>> +	}
>>>> +	writel(val, iproc_i2c->base + M_CMD_OFFSET);
>>>> +
>>>> +	time_left = wait_for_completion_timeout(&iproc_i2c->done, time_left);
>>>
>>> When the interrupt fires here after the complete timed out and before
>>> you disable the irq you still throw the result away.
>> Yes, but then this comes down to the fact that if it has reached the
>> point that is determined to be a timeout condition in the driver, one
>> should really treat it as timeout error. In a normal condition,
>> time_left should never reach zero.
> I don't agree here. I'm not sure there is a real technical reason,
> though. But still if you're in a "success after timeout already over"
> situation it's IMHO better to interpret it as success, not timeout.
> 
The thing is, the interrupt should never fire after
wait_for_completion_timeout returns zero here. If it does, then the
issue is really that the timeout value set in the driver is probably not
long enough. I just checked other I2C drivers. I think the way how
timeout is handled here is consistent with other I2C drivers.

>>>> +static int bcm_iproc_i2c_remove(struct platform_device *pdev)
>>>> +{
>>>> +	struct bcm_iproc_i2c_dev *iproc_i2c = platform_get_drvdata(pdev);
>>>> +
>>>> +	i2c_del_adapter(&iproc_i2c->adapter);
>>> You need to free the irq before i2c_del_adapter.
>>>
>> Yes. Thanks. Change back to use devm_request_irq, and use disable_irq
>> here before removing the adapter.
> The more lightweight approach is to set your device's irq-enable
> register to zero and call synchronize_irq. (For a shared irq calling
> disable_irq is even wrong here.)
> 
The fact that IRQF_SHARED flag is not set indicates this is a dedicated
IRQ line, so I thought using disable_irq here makes sense. But if both
you and Wolfram think masking all I2C interrupts at the block level +
synchronize_irq is a better approach, I can change to that. Thanks!

> Best regards
> Uwe
> 
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