linux-kernel - Re: [PATCH v3 2/3] iio: accel: Support Kionix/ROHM KX022A accelerometer

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <eb6ce47a-ab87-8a98-7ffe-b8cc50f8a549@gmail.com>
Date:   Fri, 21 Oct 2022 14:02:08 +0300
From:   Matti Vaittinen <mazziesaccount@...il.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Matti Vaittinen <matti.vaittinen@...rohmeurope.com>,
        Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Nikita Yushchenko <nikita.yoush@...entembedded.com>,
        Dmitry Rokosov <DDRokosov@...rdevices.ru>,
        Jagath Jog J <jagathjog1996@...il.com>,
        Cosmin Tanislav <demonsingur@...il.com>,
        linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/3] iio: accel: Support Kionix/ROHM KX022A
 accelerometer

On 10/21/22 13:49, Andy Shevchenko wrote:
> On Fri, Oct 21, 2022 at 10:10:08AM +0300, Matti Vaittinen wrote:
>> On 10/20/22 17:34, Andy Shevchenko wrote:
>>> On Thu, Oct 20, 2022 at 02:37:15PM +0300, Matti Vaittinen wrote:
> 
> ...
> 
>>>> +	ret = regmap_bulk_read(data->regmap, chan->address, &data->buffer,
>>>> +			       sizeof(__le16));
>>>> +	if (ret)
>>>> +		return ret;
>>>> +
>>>> +	*val = le16_to_cpu(data->buffer[0]);
>>>
>>> 'p'-variant of the above would look better
>>>
>>> 	*val = le16_to_cpup(data->buffer);
>>>
>>> since it will be the same as above address without any additional arithmetics.
>>>
>>
>> I guess there is no significant performance difference? To my eye the
>> le16_to_cpu(data->buffer[0]) is much more clear. I see right from the call
>> that we have an array here and use the first member. If there is no obvious
>> technical merit for using le16_to_cpup(data->buffer) over
>> le16_to_cpu(data->buffer[0]), then I do really prefer the latter for
>> clarity.
> 
> Then you probably wanted to have &data->buffer[0] as a parameter to
> regmap_bulk_read()?

Yes! Thanks.

> 
> ...
> 
>>>> +	if (data->trigger_enabled) {
>>>> +		iio_trigger_poll_chained(data->trig);
>>>> +		ret = IRQ_HANDLED;
>>>> +	}
>>>> +
>>>> +	if (data->state & KX022A_STATE_FIFO) {
>>>
>>>> +		ret = __kx022a_fifo_flush(idev, KX022A_FIFO_LENGTH, true);
>>>> +		if (ret > 0)
>>>> +			ret = IRQ_HANDLED;
>>>
>>> I don't like it. Perhaps
>>>
>>> 	bool handled = false;
>>> 	int ret;
>>>
>>> 	...
>>> 		ret = ...
>>> 		if (ret > 0)
>>> 			handled = true;
>>> 	...
>>>
>>> 	return IRQ_RETVAL(handled);
>>
>> I don't see the benefit of adding another variable 'handled'.
>> If I understand correctly, it just introduces one extra 'if' in IRQ thread
>> handling while hiding the return value in IRQ_RETVAL() - macro.
>>
>> I do like seeing the IRQ_NONE being returned by default and IRQ_HANDLED only
>> when "handlers" are successfully executed. Adding extra variable just
>> obfuscates this (from my eyes) while adding also the additional 'if'.
> 
> You assigning semantically different values to the same variable inside the
> function.

Ah, yes! This was really a bug making it way in. I guess you may just 
have saved me from some not-that-funny debugging session... Well spotted!

I still don't like hiding the IRQ_HANDLED / IRQ_NONE. I'll just go for

         if (data->state & KX022A_STATE_FIFO) { 

                 int ok; 

 

                 ok = __kx022a_fifo_flush(idev, KX022A_FIFO_LENGTH, 
true);
                 if (ok > 0) 

                         ret = IRQ_HANDLED; 

         }

for v4. (Which I try to send still today before my memory is flushed by 
the weekend :])

Thanks a lot!

Yours
	-- Matti

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

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