Messages in this thread | | | Date | Tue, 9 Apr 2024 15:26:18 +0100 | From | Conor Dooley <> | Subject | Re: [PATCH v2 2/3] clocksource/drivers/timer-clint: Add option to use CSR instead of mtime |
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On Sat, Apr 06, 2024 at 07:21:58PM +0800, Jisheng Zhang wrote: > As pointed out by commit ca7810aecdba ("lib: utils/timer: mtimer: add a > quirk for lacking mtime register") of opensbi: > > "T-Head developers surely have a different understanding of time CSR and > CLINT's mtime register with SiFive ones, that they did not implement > the mtime register at all -- as shown in openC906 source code, their > time CSR value is just exposed at the top of their processor IP block > and expects an external continous counter, which makes it not > overrideable, and thus mtime register is not implemented, even not for > reading. However, if CLINTEE is not enabled in T-Head's MXSTATUS > extended CSR, these systems still rely on the mtimecmp registers to > generate timer interrupts. This makes it necessary to implement T-Head > C9xx CLINT support in OpenSBI MTIMER driver, which skips implementing > reading mtime register and falls back to default code that reads time > CSR." > > To use the clint in RISCV-M NOMMU env on Milkv Duo little core, we > need to fall back to read time CSR instead of mtime register. Add the > option for this purpose. > > Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
> diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig > index 34faa0320ece..7bbdbf2f96a8 100644 > --- a/drivers/clocksource/Kconfig > +++ b/drivers/clocksource/Kconfig > @@ -650,6 +650,15 @@ config CLINT_TIMER > This option enables the CLINT timer for RISC-V systems. The CLINT > driver is usually used for NoMMU RISC-V systems. > > +config CLINT_USE_CSR_INSTEADOF_MTIME > + bool "Use TIME CSR instead of the mtime register" > + depends on CLINT_TIMER > + help > + Use TIME CSR instead of mtime register. Enable this option if > + prefer TIME CSR over MTIME register, or if the implementation > + doesn't implement the mtime register in CLINT, so fall back on > + TIME CSR.
This, as a Kconfig option, seems a bit strange to me. We know at runtime if we are on a T-Head device without the mtime register and should be able decide to use the CSR implementation dynamically in that case, right? [unhandled content-type:application/pgp-signature] | |