linux-kernel - Re: [PATCH 1/4] i2c: tegra: make sure register writes completes

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Date:	Tue, 12 Jun 2012 15:46:41 +0530
From:	Laxman Dewangan <ldewangan@...dia.com>
To:	Wolfram Sang <w.sang@...gutronix.de>
CC:	"khali@...ux-fr.org" <khali@...ux-fr.org>,
	"ben-linux@...ff.org" <ben-linux@...ff.org>,
	"swarren@...dotorg.org" <swarren@...dotorg.org>,
	"olof@...om.net" <olof@...om.net>,
	"linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH 1/4] i2c: tegra: make sure register writes completes

On Tuesday 12 June 2012 01:24 PM, Wolfram Sang wrote:
> * PGP Signed by an unknown key
>
> On Tue, Jun 05, 2012 at 06:39:57PM +0530, Laxman Dewangan wrote:
>> @@ -430,6 +430,13 @@ static irqreturn_t tegra_i2c_isr(int irq, void *dev_id)
>>   	if (i2c_dev->is_dvc)
>>   		dvc_writel(i2c_dev, DVC_STATUS_I2C_DONE_INTR, DVC_STATUS);
>>
>> +	/*
>> +	 * Register write get queued in the PPSB bus and write can
>> +	 * happen later. Read back register to make sure that register
>> +	 * write is completed.
>> +	 */
>> +	i2c_readl(i2c_dev, I2C_INT_STATUS);
> Does it make sense to put the read into i2c_writel?
>
We can not put in i2c_writel() as we also do fifo write using this and 
writing and reading back fifo can drainout the fifo.
hence putting this here seems more appropriate.
>> +
>>   	if (status&  I2C_INT_PACKET_XFER_COMPLETE) {
>>   		BUG_ON(i2c_dev->msg_buf_remaining);
>>   		complete(&i2c_dev->msg_complete);
>> @@ -444,6 +451,9 @@ err:
>>   	if (i2c_dev->is_dvc)
>>   		dvc_writel(i2c_dev, DVC_STATUS_I2C_DONE_INTR, DVC_STATUS);
>>
>> +	/* Read back register to make sure that register writes completed */
>> +	i2c_readl(i2c_dev, I2C_INT_STATUS);
>> +
>>   	complete(&i2c_dev->msg_complete);
>>   	return IRQ_HANDLED;
>>   }
>> @@ -505,6 +515,9 @@ static int tegra_i2c_xfer_msg(struct tegra_i2c_dev *i2c_dev,
>>   	ret = wait_for_completion_timeout(&i2c_dev->msg_complete, TEGRA_I2C_TIMEOUT);
>>   	tegra_i2c_mask_irq(i2c_dev, int_mask);
>>
>> +	/* Read back register to make sure that register writes completed */
>> +	i2c_readl(i2c_dev, I2C_INT_MASK);
>> +
> It definately makes sense to put this read into tegra_i2c_mask_irq()?
>
Ok, fine with me. I put the read back logic inside mask_irq() and 
unmask_irq().
Will send the fix in next patch.
>>   	if (WARN_ON(ret == 0)) {
>>   		dev_err(i2c_dev->dev, "i2c transfer timed out\n");
> Regards,
>
>     Wolfram
>

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