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

[Kuan-Wei Chiu <visitorckw@gmail.com>]

Hi Yao,

On Wed, Dec 31, 2025 at 06:27:49AM +0000, Yao Zi wrote:
> 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?

My apologies, I should have remembered that.
I will sort the headers in the next version.

> 
> > +/* 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).

Agreed.
I will add a comment explaining this.

> 
> > +	time = ((u64)high << 32) | low;
> > +
> > +	return time;
> > +}
> 
> With the header sorted,
> 
> Reviewed-by: Yao Zi <me@ziyao.cc>

Thanks for the review!

Regards,
Kuan-Wei