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Re: [PATCH] xen/arm: Validate generic timer frequency
- To: Michal Orzel <michal.orzel@xxxxxxx>
- From: Luca Fancellu <Luca.Fancellu@xxxxxxx>
- Date: Thu, 28 Sep 2023 14:02:17 +0000
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- Cc: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Bertrand Marquis <Bertrand.Marquis@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
- Delivery-date: Thu, 28 Sep 2023 14:02:44 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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- Thread-topic: [PATCH] xen/arm: Validate generic timer frequency
> On 28 Sep 2023, at 13:34, Michal Orzel <michal.orzel@xxxxxxx> 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>
> ---
Reviewed-by: Luca Fancellu <luca.fancellu@xxxxxxx>
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