Re: [PATCH] xen/arm: Validate generic timer frequency

[Julien Grall <julien@xxxxxxx>]

Hi Michal,

On 28/09/2023 13:34, Michal Orzel wrote:
> Generic timer dt node property "clock-frequency" (refer Linux dt binding
> Documentation/devicetree/bindings/timer/arm,arch_timer.yaml) is used to
> override the incorrect value set by firmware in CNTFRQ_EL0. If the value
> of this property is 0 (i.e. by mistake), Xen would continue to work and
> use the value from the sysreg instead. The logic is thus incorrect and
> results in inconsistency when creating timer node for domUs:
>   - libxl domUs: clock_frequency member of struct xen_arch_domainconfig
>     is set to 0 and libxl ignores setting the "clock-frequency" property,
>   - dom0less domUs: "clock-frequency" property is taken from dt_host and
>     thus set to 0.
>
> Property "clock-frequency" is used to override the value from sysreg,
> so if it is also invalid, there is nothing we can do and we shall panic
> to let user know about incorrect setting. Going even further, we operate
> under assumption that the frequency must be at least 1KHz (i.e. cpu_khz
> not 0) in order for Xen to boot. Therefore, introduce a new helper
> validate_timer_frequency() to verify this assumption and use it to check
> the frequency obtained either from dt property or from sysreg.
>
> Signed-off-by: Michal Orzel <michal.orzel@xxxxxxx>
Acked-by: Julien Grall <jgrall@xxxxxxxxxx>

Cheers,

--
Julien Grall