linux-kernel - Re: [PATCH 2/2] drivers/perf: riscv_pmu_sbi: add support for PMU variant on T-Head C9xx cores

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Date:   Wed, 5 Oct 2022 19:38:59 +0200
From:   Andrew Jones <ajones@...tanamicro.com>
To:     Heiko Stuebner <heiko@...ech.de>
Cc:     atishp@...shpatra.org, anup@...infault.org, will@...nel.org,
        mark.rutland@....com, paul.walmsley@...ive.com, palmer@...belt.com,
        aou@...s.berkeley.edu, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org, Conor.Dooley@...rochip.com,
        cmuellner@...ux.com, samuel@...lland.org
Subject: Re: [PATCH 2/2] drivers/perf: riscv_pmu_sbi: add support for PMU
 variant on T-Head C9xx cores

On Tue, Oct 04, 2022 at 10:37:24PM +0200, Heiko Stuebner wrote:
> With the T-HEAD C9XX cores being designed before or during the ratification
> to the SSCOFPMF extension, it implements functionality very similar but
> not equal to it.
> 
> It implements overflow handling and also some privilege-mode filtering.
> While SSCOFPMF supports this for all modes, the C9XX only implements the
> filtering for M-mode and S-mode but not user-mode.
> 
> So add some adaptions to allow the C9XX to still handle
> its PMU through the regular SBI PMU interface instead of defining new
> interfaces or drivers.
> 
> To work properly, this requires a matching change in SBI, though the actual
> interface between kernel and SBI does not change.
> 
> The main differences are a the overflow CSR and irq number.
> 
> As the reading of the overflow-csr is in the hot-path during irq handling,
> use an errata and alternatives to not introduce new conditionals there.
> 
> Signed-off-by: Heiko Stuebner <heiko@...ech.de>
> ---
>  arch/riscv/Kconfig.erratas           | 13 +++++++++++
>  arch/riscv/errata/thead/errata.c     | 18 +++++++++++++++
>  arch/riscv/include/asm/errata_list.h | 16 +++++++++++++-
>  drivers/perf/riscv_pmu_sbi.c         | 33 +++++++++++++++++++---------
>  4 files changed, 69 insertions(+), 11 deletions(-)

Reviewed-by: Andrew Jones <ajones@...tanamicro.com>