Re: [PATCH v6] hwmon: add driver for ARCTIC Fan Controller

["Thomas Weißschuh" <linux@weissschuh.net>]

Hi Aureo,

On 2026-04-01 23:39:47+0800, Aureo Serrano de Souza wrote:
(...)

> +struct arctic_fan_data {
> +	struct hid_device *hdev;
> +	struct device *hwmon_dev;	/* stored for explicit unregister in remove() */
> +	spinlock_t in_report_lock;	/* protects fan_rpm, ack_status, write_pending, pwm_duty */
> +	struct completion in_report_received; /* ACK (ID 0x02) received in raw_event */
> +	int ack_status;			/* 0 = OK, negative errno on device error */
> +	bool write_pending;		/* true while an OUT report ACK is in flight */
> +	u32 fan_rpm[ARCTIC_NUM_FANS];
> +	u8 pwm_duty[ARCTIC_NUM_FANS];	/* 0-255 matching sysfs range; converted to 0-100 on send */
> +	/*
> +	 * OUT report buffer. Cache-line aligned so it occupies its own cache
> +	 * line, preventing DMA cache-coherency issues with adjacent fields
> +	 * (fan_rpm[], pwm_duty[]) on non-coherent architectures.
> +	 * Embedded in the devm_kzalloc'd struct so it is heap-allocated and
> +	 * passes usb_hcd_map_urb_for_dma(). Serialized by the hwmon core.
> +	 */
> +	u8 buf[ARCTIC_REPORT_LEN] ____cacheline_aligned;

I recently discovered __dma_from_device_group_begin() / _end().
These look like the correct solution to use here. It would also make
parts of the comment unnecessary, as the macro already expresses this
semantic.

> +};

(...)


Thomas