linux-kernel - Re: [PATCH RESEND] irqchip: riscv: Order normal writes and IPI writes

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Message-ID: <87plk88s1o.ffs@tglx>
Date: Mon, 27 Jan 2025 11:33:39 +0100
From: Thomas Gleixner <tglx@...utronix.de>
To: Xu Lu <luxu.kernel@...edance.com>, anup@...infault.org,
 charlie@...osinc.com, paul.walmsley@...ive.com, palmer@...belt.com
Cc: lihangjing@...edance.com, xieyongji@...edance.com,
 linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org, Xu Lu
 <luxu.kernel@...edance.com>
Subject: Re: [PATCH RESEND] irqchip: riscv: Order normal writes and IPI writes

On Mon, Jan 27 2025 at 17:38, Xu Lu wrote:

This is not a RESEND. The change log has been modified, no?

The prefix is incorrect. See

  https://www.kernel.org/doc/html/latest/process/maintainer-tip.html

> RISC-V distinguishes between normal memory accesses and device I/O and

What is a normal memory write? Are there abnormal memory writes too?

> uses FENCE instruction to order them as viewed by othe RISC-V harts and
> external devices or coprocessors. The FENCE instruction can order any
> combination of device input(I), device output(O), memory reads(R) and
> memory writes(W). For example, 'fence w, o' can be used to ensure all

Can be? It _is_ used, no?

> memory writes from instructions preceding the FENCE instruction appear
> earlier in the global memory order than device output writes from
> instructions after the FENCE instruction.
>
> RISC-V issues IPI by writing certain value to IMSIC/ACLINT MMIO
> registers, which is regarded as device output operation. However, the
> existing implementation of IMSIC/ACLINT driver issues IPI via
> writel_relaxed(), which does not guarantee the order of device output
> operation and preceding memory writes. Then the hart receiving IPI may
> not have seen the latest data yet.
>
> This commit fixes this by replacing writel_relaxed() with writel()
> when

'This commit' is equally wrong as 'This patch'. See Documentation/process/

> issuing IPI, which will use 'fence w, o' to ensure all previous writes
> made by current hart are visible to other harts before they receive
> the IPI.

I've fixed it up for you.

Thanks,

        tglx