Re: [PATCH v5 03/11] platform: cznic: turris-omnia-mcu: Add support for MCU connected GPIOs

[Matti Vaittinen <mazziesaccount@gmail.com>]

On 3/25/24 11:53, Marek Behún wrote:
> On Mon, 25 Mar 2024 11:10:04 +0200
> Matti Vaittinen <mazziesaccount@gmail.com> wrote:
> 
>> Hi Marek,
>>
>> I can't say I did a proper review but browsing through the code without
>> proper understanding of the platform raised one small question :)
>>
>> On 3/23/24 18:43, Marek Behún wrote:
>>> Add support for GPIOs connected to the MCU on the Turris Omnia board.
>>>
>>> This includes:
>>> - front button pin
>>> - enable pins for USB regulators
>>> - MiniPCIe / mSATA card presence pins in MiniPCIe port 0
>>> - LED output pins from WAN ethernet PHY, LAN switch and MiniPCIe ports
>>> - on board revisions 32+ also various peripheral resets and another
>>>     voltage regulator enable pin
>>>
>>> Signed-off-by: Marek Behún <kabel@kernel.org>
>>
>> ...
>>
>>> +/**
>>> + * omnia_mask_interleave - Interleaves the bytes from @rising and @falling
>>> + *	@dst: the destination u8 array of interleaved bytes
>>> + *	@rising: rising mask
>>> + *	@falling: falling mask
>>> + *
>>> + * Interleaves the little-endian bytes from @rising and @falling words.
>> This means the 'rising' and 'falling' should always be little-endian?
>> Should the parameter types reflect this? Or should we see some
>> cpu_to_le() calls? (Or, is this code just guaranteed to be always
>> running on a le-machine?).
>>
>>> + * If @rising = (r0, r1, r2, r3) and @falling = (f0, f1, f2, f3), the result is
>>> + * @dst = (r0, f0, r1, f1, r2, f2, r3, f3).
>>> + *
>>> + * The MCU receives interrupt mask and reports pending interrupt bitmap int this
>>> + * interleaved format. The rationale behind it is that the low-indexed bits are
>>> + * more important - in many cases, the user will be interested only in
>>> + * interrupts with indexes 0 to 7, and so the system can stop reading after
>>> + * first 2 bytes (r0, f0), to save time on the slow I2C bus.
>>> + *
>>> + * Feel free to remove this function and its inverse, omnia_mask_deinterleave,
>>> + * and use an appropriate bitmap_* function once such a function exists.
>>> + */
>>> +static void omnia_mask_interleave(u8 *dst, u32 rising, u32 falling)
>>> +{
>>> +	for (int i = 0; i < sizeof(u32); ++i) {
>>> +		dst[2 * i] = rising >> (8 * i);
>>> +		dst[2 * i + 1] = falling >> (8 * i);
>>> +	}
>>> +}
>>> +
>>> +/**
>>> + * omnia_mask_deinterleave - Deinterleaves the bytes into @rising and @falling
>>> + *	@src: the source u8 array containing the interleaved bytes
>>> + *	@rising: pointer where to store the rising mask gathered from @src
>>> + *	@falling: pointer where to store the falling mask gathered from @src
>>> + *
>>> + * This is the inverse function to omnia_mask_interleave.
>>> + */
>>> +static void omnia_mask_deinterleave(const u8 *src, u32 *rising, u32 *falling)
>>> +{
>>> +	*rising = *falling = 0;
>>> +
>>> +	for (int i = 0; i < sizeof(u32); ++i) {
>>> +		*rising |= src[2 * i] << (8 * i);
>>> +		*falling |= src[2 * i + 1] << (8 * i);
>>> +	}
>>
>> Also here I could expect seeing le_to_cpu() unless I am (again :])
>> missing something.
> 
> I don't understand. The rising and falling variables have native
> endiannes, as they should have.

So, it was the last option then :) I was missing something.

> And the src and dst are u8 arrays, which contain two LE32
> unsigned integers, but these integers are interleaved. I am converting
> then to two native unsigned integers byte by byte, so I am basically
> doing what a theoretical le32_interleaved_le32_to_cpu() would have done
> if it did exist. Putting another le*_to_cpu() would only break things.

Thank you for the explanation. I commented way too hastily after a 
glance - missing the point you used shift and not u8 pointer to go 
through the 'rising' and 'falling' in interleave() - and the point that 
the result of deinterleave() was u8s. Very sorry for the noise.

Thanks for the patience!

Yours,
	-- Matti

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

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