Re: [PATCH v3 2/6] timer: Add Goldfish timer driver

[Yao Zi <me@ziyao.cc>]

On Tue, Dec 30, 2025 at 04:01:08PM +0000, Kuan-Wei Chiu wrote:
> Add support for the Goldfish timer driver. This driver utilizes the
> Goldfish RTC hardware to provide a nanosecond-resolution timer. This
> virtual device is commonly found in QEMU virtual machines (such as the
> m68k virt machine) and Android emulators.
> 
> The driver implements the standard U-Boot timer UCLASS interface,
> exposing a 64-bit monotonically increasing counter with a 1GHz clock
> rate derived from the RTC registers.
> 
> Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
> ---
> Changes in v3:
> - New patch.
> 
> The link provided by Daniel [1] returned a 404 error.
> Since the implementation is straightforward, I wrote this driver from
> scratch.
> 
> [1]: https://github.com/fifteenhex/u-boot/blob/mc68000/drivers/rtc/goldfish_timer.c

...

> diff --git a/drivers/timer/goldfish_timer.c b/drivers/timer/goldfish_timer.c
> new file mode 100644
> index 00000000000..8205ac77853
> --- /dev/null
> +++ b/drivers/timer/goldfish_timer.c
> @@ -0,0 +1,60 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * Copyright (C) 2025, Kuan-Wei Chiu <visitorckw@gmail.com>
> + *
> + * Goldfish Timer driver
> + */
> +
> +#include <dm.h>
> +#include <timer.h>
> +#include <asm/io.h>
> +#include <linux/errno.h>
> +#include <goldfish_timer.h>

Sort the headers?

> +/* Goldfish RTC registers used as Timer */
> +#define TIMER_TIME_LOW	0x00
> +#define TIMER_TIME_HIGH	0x04
> +
> +static u64 goldfish_timer_get_count(struct udevice *dev)
> +{
> +	struct goldfish_timer_plat *plat = dev_get_plat(dev);
> +	u32 low, high;
> +	u64 time;
> +
> +	/*
> +	 * Goldfish RTC provides time in nanoseconds.
> +	 * We read the high 32-bits and low 32-bits to construct the 64-bit value.
> +	 */
> +	low = readl(plat->base + TIMER_TIME_LOW);
> +	high = readl(plat->base + TIMER_TIME_HIGH);

It may be worth a comment to point out that the value of TIMER_TIME_HIGH
only updates when TIMER_TIME_LOW is read, so it's impossible to read out
teared values (higher half has been updated after lower half is read).

> +	time = ((u64)high << 32) | low;
> +
> +	return time;
> +}

With the header sorted,

Reviewed-by: Yao Zi <me@ziyao.cc>

Regards,
Yao Zi