Received-SPF: pass (google.com: domain of linux-kernel+bounces-86720-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:4601:e00::3 as permitted sender) client-ip=2604:1380:4601:e00::3;
Message-ID: <21ecfb62-30b7-4073-bad6-46a9e08e08b0@gmail.com>
Date: Thu, 29 Feb 2024 14:58:52 +0200
Precedence: bulk
MIME-Version: 1.0
User-Agent: Mozilla Thunderbird
Subject: Re: [PATCH v8 5/5] iio: light: Add support for APDS9306 Light Sensor
Content-Language: en-US, en-GB
To: Subhajit Ghosh <subhajit.ghosh@tweaklogic.com>,
 Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Jonathan Cameron <jic23@kernel.org>, Lars-Peter Clausen
 <lars@metafoo.de>, Rob Herring <robh+dt@kernel.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
 Conor Dooley <conor+dt@kernel.org>, Marek Vasut <marex@denx.de>,
 Anshul Dalal <anshulusr@gmail.com>,
 Javier Carrasco <javier.carrasco.cruz@gmail.com>,
 Matt Ranostay <matt@ranostay.sg>,
 Stefan Windfeldt-Prytz <stefan.windfeldt-prytz@axis.com>,
 linux-iio@vger.kernel.org, devicetree@vger.kernel.org,
 linux-kernel@vger.kernel.org
References: <20240228122408.18619-1-subhajit.ghosh@tweaklogic.com>
 <20240228122408.18619-6-subhajit.ghosh@tweaklogic.com>
 <a828e77c-b3d4-49bb-b0bb-b9fd6cb7d114@gmail.com>
 <Zd9tApJClX7Frq20@smile.fi.intel.com>
 <45386f39-a034-4d70-a6d4-8804c27aadce@tweaklogic.com>
From: Matti Vaittinen <mazziesaccount@gmail.com>
In-Reply-To: <45386f39-a034-4d70-a6d4-8804c27aadce@tweaklogic.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit

On 2/29/24 14:34, Subhajit Ghosh wrote:
> On 29/2/24 03:57, Andy Shevchenko wrote:
>> On Wed, Feb 28, 2024 at 03:08:56PM +0200, Matti Vaittinen wrote:
>>> On 2/28/24 14:24, Subhajit Ghosh wrote:
>>
>> ...
>>
>>>> +    ret = iio_gts_find_new_gain_by_old_gain_time(&data->gts, gain_old,
>>>> +                             intg_old, val2, &gain_new);
>>>
>>> You don't use the 'ret' here, so maybe for the clarity, not assign it.
>>> Or, maybe you wan't to try to squeeze out few cycles for succesful 
>>> case and
>>> check the ret for '0' - in which case you should be able to omit the 
>>> check
>>> right below as well as the call to iio_find_closest_gain_low(). OTOH, 
>>> this
>>> is likely not a "hot path" so I don't care too much about the extra 
>>> call if
>>> you think code is clearer this way.
>>>
>>>> +    if (gain_new < 0) {
>>>> +        dev_err_ratelimited(dev, "Unsupported gain with time\n");
>>>> +        return gain_new;
>>>> +    }
>>
>> What is the difference between negative response from the function 
>> itself and
>> similar in gain_new?
>>
> -ve response form the function is an error condition.
> -ve value in gain_new means - no valid gains could be computed.
> In case of error conditions from the function, the gain_new is also set 
> to -1.
> My use case is valid hardware gain so I went for checking only gain_new.
> Matti will be the best person to answer on this.

I now rely on the kerneldoc for the
iio_gts_find_new_gain_by_old_gain_time() as it seems reasonable to me:

* Return: 0 if an exactly matching supported new gain was found. When a
* non-zero value is returned, the @new_gain will be set to a negative or
* positive value. The negative value means that no gain could be computed.
* Positive value will be the "best possible new gain there could be". There
* can be two reasons why finding the "best possible" new gain is not deemed
* successful. 1) This new value cannot be supported by the hardware. 2) 
The new
* gain required to maintain the scale would not be an integer. In this case,
* the "best possible" new gain will be a floored optimal gain, which may or
* may not be supported by the hardware.

Eg, if ret is zero, there is no need to check validity of the gain_new 
but it is guaranteed to be one of the supported gains.

Yours,
	-- Matti

-- 
Matti Vaittinen
Linux kernel developer at ROHM Semiconductors
Oulu Finland

~~ When things go utterly wrong vim users can always type :help! ~~