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

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Message-ID: <d216f201-183f-c253-495d-1d9203141a63@quicinc.com>
Date:   Mon, 22 Nov 2021 21:13:30 +0530
From:   Sai Prakash Ranjan <quic_saipraka@...cinc.com>
To:     Arnd Bergmann <arnd@...db.de>
CC:     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 11/22/2021 9:05 PM, Arnd Bergmann wrote:
> 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()
>
>

Sure, will do that.

Thanks,
Sai