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Subject: Re: [PATCH 4.19 309/639] hwmon: (w83627hf) Use request_muxed_region
 for Super-IO accesses
To:     Pavel Machek <pavel@denx.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     linux-kernel@vger.kernel.org, stable@vger.kernel.org,
        Sasha Levin <sashal@kernel.org>
References: <20200124093047.008739095@linuxfoundation.org>
 <20200124093125.642179022@linuxfoundation.org>
 <20200125185935.GF14064@duo.ucw.cz>
From:   Guenter Roeck <linux@roeck-us.net>
Message-ID: <9639ba77-ece0-d825-a1b0-cbf8b45af3ab@roeck-us.net>
Date:   Sat, 25 Jan 2020 11:14:57 -0800
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On 1/25/20 10:59 AM, Pavel Machek wrote:
> Hi!
>> [ Upstream commit e95fd518d05bfc087da6fcdea4900a57cfb083bd ]
>>
>> Super-IO accesses may fail on a system with no or unmapped LPC bus.
>>
>> Also, other drivers may attempt to access the LPC bus at the same time,
>> resulting in undefined behavior.
>>
>> Use request_muxed_region() to ensure that IO access on the requested
>> address space is supported, and to ensure that access by multiple drivers
>> is synchronized.
>>
> 
>> @@ -1644,9 +1654,21 @@ static int w83627thf_read_gpio5(struct platform_device *pdev)
>>   	struct w83627hf_sio_data *sio_data = dev_get_platdata(&pdev->dev);
>>   	int res = 0xff, sel;
>>   
>> -	superio_enter(sio_data);
>> +	if (superio_enter(sio_data)) {
>> +		/*
>> +		 * Some other driver reserved the address space for itself.
>> +		 * We don't want to fail driver instantiation because of that,
>> +		 * so display a warning and keep going.
>> +		 */
>> +		dev_warn(&pdev->dev,
>> +			 "Can not read VID data: Failed to enable SuperIO access\n");
>> +		return res;
>> +	}
>> +
>>   	superio_select(sio_data, W83627HF_LD_GPIO5);
>>   
>> +	res = 0xff;
>> +
> 
> This is strange. res is not actually assigned in the code above, so we
> have res = 0xff twice. Can we remove one of the initializations and do
> 'return 0xff' directly to make code more clear?
> 
> 
>> @@ -1677,7 +1699,17 @@ static int w83687thf_read_vid(struct platform_device *pdev)
>>   	struct w83627hf_sio_data *sio_data = dev_get_platdata(&pdev->dev);
>>   	int res = 0xff;
>>   
>> -	superio_enter(sio_data);
>> +	if (superio_enter(sio_data)) {
>> +		/*
>> +		 * Some other driver reserved the address space for itself.
>> +		 * We don't want to fail driver instantiation because of that,
>> +		 * so display a warning and keep going.
>> +		 */
>> +		dev_warn(&pdev->dev,
>> +			 "Can not read VID data: Failed to enable SuperIO access\n");
>> +		return res;
>> +	}
> 
> Direct "return 0xff" would make more sense here, too.
> 

Please feel free to submit a patch to improve the upstream code.

Thanks,
Guenter