linux-kernel - Re: [PATCH v2 11/35] nds32: Device specific operations

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Date:   Mon, 27 Nov 2017 15:51:31 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Greentime Hu <green.hu@...il.com>
Cc:     Greentime <greentime@...estech.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Marc Zyngier <marc.zyngier@....com>,
        Rob Herring <robh+dt@...nel.org>,
        Networking <netdev@...r.kernel.org>,
        Vincent Chen <deanbo422@...il.com>,
        DTML <devicetree@...r.kernel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        David Howells <dhowells@...hat.com>,
        Will Deacon <will.deacon@....com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        linux-serial@...r.kernel.org, Vincent Chen <vincentc@...estech.com>
Subject: Re: [PATCH v2 11/35] nds32: Device specific operations

On Mon, Nov 27, 2017 at 1:27 PM, Greentime Hu <green.hu@...il.com> wrote:
> From: Greentime Hu <greentime@...estech.com>
>
> This patch introduces ioremap implementations.
>
> Signed-off-by: Vincent Chen <vincentc@...estech.com>
> Signed-off-by: Greentime Hu <greentime@...estech.com>
> ---
>  arch/nds32/include/asm/io.h |   25 +++++++++++++++
>  arch/nds32/mm/ioremap.c     |   75 +++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 100 insertions(+)
>  create mode 100644 arch/nds32/include/asm/io.h
>  create mode 100644 arch/nds32/mm/ioremap.c
>
> diff --git a/arch/nds32/include/asm/io.h b/arch/nds32/include/asm/io.h
> new file mode 100644
> index 0000000..b83dea1
> --- /dev/null
> +++ b/arch/nds32/include/asm/io.h
> @@ -0,0 +1,25 @@

> +#ifndef __ASM_NDS32_IO_H
> +#define __ASM_NDS32_IO_H
> +
> +#ifdef __KERNEL__
> +void iounmap(void __iomem * addr);
> +#include <asm-generic/io.h>
> +
> +#endif /* __KERNEL__ */
> +#endif /* __ASM_NDS32_IO_H */

Here, you should define a lot of the I/O accessor functions,
dereferencing a pointer
is generally not enough to guarantee an atomic MMIO operation. You need to
force the access to use the correct size to prevent the compiler from issuing
byte-sized operations when it thinks the pointer might be unaligned, and
there should be barriers that ensure a memory access is synchronized with
a DMA that might be triggered by a writel, or claimed to be completed after
a readl. Please see the risc-v header for this, it has many good explanations.

        Arnd