linux-kernel - Re: [PATCH] RISC-V: Allow drivers to provide custom read

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Message-ID: <20200904162530.GA32095@lst.de>
Date:   Fri, 4 Sep 2020 18:25:30 +0200
From:   Christoph Hellwig <hch@....de>
To:     Anup Patel <anup.patel@....com>
Cc:     Palmer Dabbelt <palmer@...belt.com>,
        Palmer Dabbelt <palmerdabbelt@...gle.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Atish Patra <atish.patra@....com>,
        Alistair Francis <Alistair.Francis@....com>,
        Christoph Hellwig <hch@....de>,
        Anup Patel <anup@...infault.org>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] RISC-V: Allow drivers to provide custom read_cycles64
 for M-mode kernel

On Fri, Sep 04, 2020 at 09:51:21PM +0530, Anup Patel wrote:
> The TIME CSR is usually not present on most RISC-V systems so the
> M-mode firmware will emulate the TIME CSR for the S-mode (MMU) kernel
> whereas the M-mode (NoMMU) kernel will have to use MMIO clocksource.
> 
> Currently, the get_cycles() implementation in asm/timex.h does not
> consider the above fact so we provide alternate implementation of
> the get_cycles() for the M-mode (NoMMU) kernel which expects drivers
> to provide custom MMIO based read_cycles64() method.

Please just go back to the previous working version without all the
crazy indirections.

The whole timer and irq code has been turned into a giant maze of
indirections lately.