linux-kernel - Re: [PATCHv4 2/2] arm64/io: Add a header for mmio access instrumentation

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Date:   Mon, 22 Nov 2021 16:35:01 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Sai Prakash Ranjan <quic_saipraka@...cinc.com>
Cc:     Arnd Bergmann <arnd@...db.de>, Will Deacon <will@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Catalin Marinas <catalin.marinas@....com>,
        quic_psodagud@...cinc.com, Marc Zyngier <maz@...nel.org>,
        gregkh <gregkh@...uxfoundation.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCHv4 2/2] arm64/io: Add a header for mmio access instrumentation

On Mon, Nov 22, 2021 at 3:59 PM Sai Prakash Ranjan
<quic_saipraka@...cinc.com> wrote:
> >> And if we do move this instrumentation to asm-generic/io.h, how will
> >> that be executed since
> >> the arch specifc read{b,w,l,q} overrides this generic version?
> > As I understand it, your version also requires architecture specific
> > changes, so that would be the same: it only works for architectures
> > that get the definition of readl()/readl_relaxed()/inl()/... from
> > include/asm-generic/io.h and only override the __raw version. Arnd
>
> Sorry, I didn't get this part, so  I am trying this on ARM64:
>
> arm64/include/asm/io.h has read{b,l,w,q} defined.
> include/asm-generic/io.h has below:
>    #ifndef readl
>    #define readl readl
>    static inline u32 readl(const volatile void __iomem *addr)
>
> and we include asm-generic/io.h in arm64/include/asm/io.h at the end
> after the definitions for arm64 mmio accesors.
> So arch implementation here overrides generic ones as I see it, am I
> missing something? I even confirmed this
> with some trace_printk to generic and arch specific definitions of readl
> and I see arch specific ones being called.

Ah, you are right that the arm64 version currently has custom definitions
of the high-level interfaces. These predate the introduction of the
__io_{p,}{b,a}{r,w} macros and are currently only used on risc-v.

I think in this case you should start by changing arm64 to use the
generic readl() etc definitions, by removing the extra definitions and
using

#define __io_ar(v) __iormb(__v)
#define __io_bw() dma_wmb()

      Arnd