Re: [PATCH 06/25] ARM: tegra: Fix compatible string for Tegra30+ timer

Thierry Reding
2021-12-13T16:04:10Z

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On Fri, Dec 10, 2021 at 06:23:34PM +0300, Dmitry Osipenko wrote:
> 10.12.2021 16:42, Thierry Reding пишет:
> > On Thu, Dec 09, 2021 at 10:36:43PM +0300, Dmitry Osipenko wrote:
> >> 09.12.2021 20:33, Thierry Reding пишет:
> >>> From: Thierry Reding <treding@nvidia.com>
> >>>
> >>> The TKE (time-keeping engine) found on Tegra30 and later is not
> >>> backwards compatible with the version found on Tegra20, so update the
> >>> compatible string list accordingly.
> >>>
> >>> Signed-off-by: Thierry Reding <treding@nvidia.com>
> >>> ---
> >>> arch/arm/boot/dts/tegra114.dtsi | 2 +-
> >>> arch/arm/boot/dts/tegra124.dtsi | 2 +-
> >>> arch/arm/boot/dts/tegra30.dtsi | 2 +-
> >>> 3 files changed, 3 insertions(+), 3 deletions(-)
> ...
> >>> timer@60005000 {
> >>> - compatible = "nvidia,tegra30-timer", "nvidia,tegra20-timer";
> >>> + compatible = "nvidia,tegra30-timer";
> >>> reg = <0x60005000 0x400>;
> >>> interrupts = <GIC_SPI 0 IRQ_TYPE_LEVEL_HIGH>,
> >>> <GIC_SPI 1 IRQ_TYPE_LEVEL_HIGH>,
> >>>
> >>
> >> What exactly is incompatible? IIRC, T30+ is a superset of T20. This
> >> patch should be wrong, also see [1].
> >
> > As the comment in that location explains, Tegra114 and later have an
> > architectural timer that is preferred over the legacy timer. So while
> > this doesn't technically make Tegra114 incompatible (in terms of
> > register programming, etc.) with Tegra20, in practice we don't want
> > Tegra20 behaviour on Tegra114 and later.
>
> So the T114 timer code works using the T20 code and we prefer to use the
> ARCH timer on T114+ in the driver, what is the problem then? Where is
> the incompatibility?

It's the priority that's set differently for Tegra20 and Tegra30. On
Tegra114 and later, the Tegra timer has lower priority so that the
architected timer takes precedence. It's not exactly an
incompatibilitity, but there's no good way to describe it otherwise.

Thierry

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