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

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Date:	Tue, 12 Jun 2012 10:07:03 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Laxman Dewangan <ldewangan@...dia.com>
CC:	Wolfram Sang <w.sang@...gutronix.de>,
	"khali@...ux-fr.org" <khali@...ux-fr.org>,
	"ben-linux@...ff.org" <ben-linux@...ff.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 06/12/2012 04:16 AM, Laxman Dewangan wrote:
> 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.

You can put it inside i2c_writel(), but make the read-back conditional
depending on which register was just written. The Tegra SD driver has
similar conditional code in readl/writel to WAR some HW quirks.
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