Re: [PATCH] mac_newworld: change timebase frequency from 100MHz to 25MHz for mac99 machine

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

On 4/3/24 08:35, Mark Cave-Ayland wrote:
> MacOS X uses multiple techniques for calibrating timers depending upon the detected
> hardware. One of these calibration routines compares the change in the timebase
> against the KeyLargo timer and uses this to recalculate the clock frequency,
> timebase frequency and bus frequency if the calibration exceeds certain limits.
> This recalibration occurs despite the correct values being passed via the device
> tree, and is likely due to buggy firmware on some hardware.
> 
> The timebase frequency of 100MHz was set way back in 2005 by commit fa296b0fb4
> ("PIC fix - changed back TB frequency to 100 MHz") and with this value on a
> mac99,via=pmu machine the OSX 10.2 timer calibration incorrectly calculates the
> bus frequency as 400MHz instead of 100MHz. The most noticeable side-effect is
> the UI appears sluggish and not very responsive for normal use.
> 
> Change the timebase frequency from 100MHz to 25MHz which matches that of a real
> G4 AGP machine (the closest match to QEMU's mac99 machine) and allows OSX 10.2
> to correctly detect all of the clock frequency, timebase frequency and bus
> frequency.
> 
> Tested on various MacOS images from OS 9.2 through to OSX 10.4, along with Linux
> and NetBSD and I was unable to find any regressions from this change.
> 
> Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
> ---
>   hw/ppc/mac_newworld.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>