linux-kernel - Re: [PATCH v12 1/7] mfd: Add core driver for Nuvoton NCT6694

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Message-ID: <12098259-32c4-4524-813e-38aeced837a0@roeck-us.net>
Date: Wed, 4 Jun 2025 05:40:44 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: Oliver Neukum <oneukum@...e.com>, a0282524688@...il.com, lee@...nel.org,
 linus.walleij@...aro.org, brgl@...ev.pl, andi.shyti@...nel.org,
 mkl@...gutronix.de, mailhol.vincent@...adoo.fr, andrew+netdev@...n.ch,
 davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
 pabeni@...hat.com, wim@...ux-watchdog.org, jdelvare@...e.com,
 alexandre.belloni@...tlin.com
Cc: linux-kernel@...r.kernel.org, linux-gpio@...r.kernel.org,
 linux-i2c@...r.kernel.org, linux-can@...r.kernel.org,
 netdev@...r.kernel.org, linux-watchdog@...r.kernel.org,
 linux-hwmon@...r.kernel.org, linux-rtc@...r.kernel.org,
 linux-usb@...r.kernel.org, Ming Yu <tmyu0@...oton.com>
Subject: Re: [PATCH v12 1/7] mfd: Add core driver for Nuvoton NCT6694

On 6/4/25 03:11, Oliver Neukum wrote:
> On 04.06.25 06:14, a0282524688@...il.com wrote:
>> From: Ming Yu <tmyu0@...oton.com>
>>
>> The Nuvoton NCT6694 provides an USB interface to the host to
>> access its features.
>>
>> Sub-devices can use the USB functions nct6694_read_msg() and
>> nct6694_write_msg() to issue a command. They can also request
>> interrupt that will be called when the USB device receives its
>> interrupt pipe.
>>
>> Signed-off-by: Ming Yu <tmyu0@...oton.com>
>> ---
...
>> +static void usb_int_callback(struct urb *urb)
>> +{
>> +    struct nct6694 *nct6694 = urb->context;
>> +    unsigned int *int_status = urb->transfer_buffer;
>> +    int ret;
>> +
>> +    switch (urb->status) {
>> +    case 0:
>> +        break;
>> +    case -ECONNRESET:
>> +    case -ENOENT:
>> +    case -ESHUTDOWN:
>> +        return;
>> +    default:
>> +        goto resubmit;
>> +    }
>> +
>> +    while (*int_status) {
>> +        int irq = __ffs(*int_status);
>> +
>> +        generic_handle_irq_safe(irq_find_mapping(nct6694->domain, irq));
>> +        *int_status &= ~BIT(irq);
>> +    }
> 
> Does modifying the byte have any benefit?
> 

Not sure if I understand the question, and assuming your question is regarding
*int_status: *int_status!=0 is the loop invariant, so, yes, modifying it does
have a benefit.

I'd be more concerned that transfer_buffer is the raw buffer, and that data
read from it is not endianness converted. That makes me wonder if and how the
code would work on a big endian system.

Guenter