Hi Doug, Olof,
IIUC, it sounds like this patch is needed from some other patches in
arm-soc. Olof was proposing to take this patch through its tree to
facilitate the integration.
Olof, is it this patch you were worried about ?
Thanks
-- Daniel
On 11/20/2014 12:01 AM, Doug Anderson wrote:
Daniel,
On Wed, Oct 8, 2014 at 12:33 AM, Sonny Rao <sonnyrao@xxxxxxxxxxxx> wrote:
From: Doug Anderson <dianders@xxxxxxxxxxxx>
Some 32-bit (ARMv7) systems are architected like this:
* The firmware doesn't know and doesn't care about hypervisor mode and
we don't want to add the complexity of hypervisor there.
* The firmware isn't involved in SMP bringup or resume.
* The ARCH timer come up with an uninitialized offset (CNTVOFF)
between the virtual and physical counters. Each core gets a
different random offset.
* The device boots in "Secure SVC" mode.
* Nothing has touched the reset value of CNTHCTL.PL1PCEN or
CNTHCTL.PL1PCTEN (both default to 1 at reset)
On systems like the above, it doesn't make sense to use the virtual
counter. There's nobody managing the offset and each time a core goes
down and comes back up it will get reinitialized to some other random
value.
This adds an optional property which can inform the kernel of this
situation, and firmware is free to remove the property if it is going
to initialize the CNTVOFF registers when each CPU comes out of reset.
Currently, the best course of action in this case is to use the
physical timer, which is why it is important that CNTHCTL hasn't been
changed from its reset value and it's a reasonable assumption given
that the firmware has never entered HYP mode.
Note that it's been said that on ARMv8 systems the firmware and
kernel really can't be architected as described above. That means
using the physical timer like this really only makes sense for ARMv7
systems.
Signed-off-by: Doug Anderson <dianders@xxxxxxxxxxxx>
Signed-off-by: Sonny Rao <sonnyrao@xxxxxxxxxxxx>
Reviewed-by: Mark Rutland <mark.rutland@xxxxxxx>
---
Changes in v2:
- Add "#ifdef CONFIG_ARM" as per Will Deacon
Changes in v3:
- change property name to arm,cntvoff-not-fw-configured and specify
that the value of CNTHCTL.PL1PC(T)EN must still be the reset value
of 1 as per Mark Rutland
Changes in v4:
- change property name to arm,cpu-registers-not-fw-configured and
specify that all cpu registers must have architected reset values
per Mark Rutland
- change from "#ifdef CONFIG_ARM" to "if (IS_ENABLED(CONFIG_ARM))" per
Arnd Bergmann
---
Documentation/devicetree/bindings/arm/arch_timer.txt | 8 ++++++++
drivers/clocksource/arm_arch_timer.c | 8 ++++++++
2 files changed, 16 insertions(+)
Do you know what the status of this patch is? This patch and Sonny's
patch at <https://patchwork.kernel.org/patch/5051901/> are needed on
Rockchip rk3288 for some specific things:
1. To make SMP happy with coreboot.
2. To (I assume) make SMP happy after S2R (no matter which firmware is
used since I don't think anyone has PSCI for rk3288).
...we still need a DTS entry atop these patches, but that's trivial to
add once these land.
Thanks!
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