linux-kernel - Re: [RESEND] i2c: imx: defer probing on dma channel request

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Message-ID: <7c702cc4-4bb6-02e8-6c2d-1686de503c85@nxp.com>
Date:   Tue, 26 Mar 2019 11:52:41 +0000
From:   Laurentiu Tudor <laurentiu.tudor@....com>
To:     Steven Price <steven.price@....com>,
        "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
        Ying Zhang <ying.zhang22455@....com>
CC:     "upstream-release@...ux.nxdi.nxp.com" 
        <upstream-release@...ux.nxdi.nxp.com>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Leo Li <leoyang.li@....com>, dl-linux-imx <linux-imx@....com>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "festevam@...il.com" <festevam@...il.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RESEND] i2c: imx: defer probing on dma channel request

Hi Steve,

Thanks for the review! Few comments inline.

On 25.03.2019 19:12, Steven Price wrote:
> On 25/03/2019 15:30, laurentiu.tudor@....com wrote:
>> From: Laurentiu Tudor <laurentiu.tudor@....com>
>>
>> If the dma controller is not yet probed, defer i2c probe.
>> The error path in probe was slightly modified (no functional change)
> 
> There is a functional change for cases like:
> 
>> 	ret = pm_runtime_get_sync(&pdev->dev);
>> 	if (ret < 0)
>> 		goto rpm_disable;
> 
> ...as rpm_disable will no longer fall through to the call of
> clk_disable_unprepare().

Good point, I missed that.

>> to avoid triggering this WARN_ON():
>> "cg-pll0-div1 already disabled
>> WARNING: CPU: 1 PID: 1 at drivers/clk/clk.c:828 clk_core_disable+0xa8/0xb0"
> 
> I'm also not sure how this WARN_ON was hit. i2c_imx_probe() calls
> clk_prepare_enable() which should increment the reference count. So it
> should always be possible to decrememt the enable_count. What am I missing?

I am no longer able to replicate this. Perhaps in the mean time changes 
in the clk core fixed this corner case.

>> Signed-off-by: Laurentiu Tudor <laurentiu.tudor@....com>
>> ---
>>   drivers/i2c/busses/i2c-imx.c | 21 +++++++++++++--------
>>   1 file changed, 13 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/i2c/busses/i2c-imx.c b/drivers/i2c/busses/i2c-imx.c
>> index 42fed40198a0..4e34b1572756 100644
>> --- a/drivers/i2c/busses/i2c-imx.c
>> +++ b/drivers/i2c/busses/i2c-imx.c
>> @@ -1111,7 +1111,8 @@ static int i2c_imx_probe(struct platform_device *pdev)
>>   				pdev->name, i2c_imx);
>>   	if (ret) {
>>   		dev_err(&pdev->dev, "can't claim irq %d\n", irq);
>> -		goto clk_disable;
>> +		clk_disable_unprepare(i2c_imx->clk);
>> +		return ret;
>>   	}
>>   
>>   	/* Init queue */
>> @@ -1161,19 +1162,25 @@ static int i2c_imx_probe(struct platform_device *pdev)
>>   	pm_runtime_mark_last_busy(&pdev->dev);
>>   	pm_runtime_put_autosuspend(&pdev->dev);
>>   
>> +	/* Init DMA config if supported */
>> +	ret = i2c_imx_dma_request(i2c_imx, phy_addr);
>> +	if (ret) {
>> +		if (ret != -EPROBE_DEFER)
>> +			dev_info(&pdev->dev, "can't use DMA, using PIO instead.\n");
>> +		else
>> +			goto del_adapter;
>> +	}
>> +
> 
> This can be simplified by reversing the condition:

Well, in the mean time I just found out that this commit [1] fixes the 
issue I was seeing so I think the patch is no longer needed.

[1] 
https://git.kernel.org/pub/scm/linux/kernel/git/wsa/linux.git/commit/?h=i2c/for-next&id=e1ab9a468e3b1

---
Best Regards, Laurentiu