linux-kernel - Re: [PATCH 24/31] nds32: Miscellaneous header files

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Message-ID: <CAK8P3a2uZSXr9hT=Jzu1a8Lbg3302-FOr-mtHvY_5xewyoW-jA@mail.gmail.com>
Date:   Wed, 8 Nov 2017 10:57:41 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Greentime Hu <green.hu@...il.com>
Cc:     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 <vincentc@...estech.com>
Subject: Re: [PATCH 24/31] nds32: Miscellaneous header files

On Wed, Nov 8, 2017 at 6:55 AM, Greentime Hu <green.hu@...il.com> wrote:
> +
> +static inline void __delay(unsigned long loops)
> +{
> +       __asm__ __volatile__(".align 2\n"
> +                            "1:\n"
> +                            "\taddi\t%0, %0, -1\n"
> +                            "\tbgtz\t%0, 1b\n"
> +                            :"=r"(loops)
> +                            :"0"(loops));
> +}

Does the architecture define a high-resolution clock source? If yes,
then it's better
to use that to get exact timing than to rely on the loop calibration.

> +/*
> + * This file is generally used by user-level software, so you need to
> + * be a little careful about namespace pollution etc.  Also, we cannot
> + * assume GCC is being used.
> + */
> +
> +typedef unsigned short __kernel_mode_t;
> +#define __kernel_mode_t __kernel_mode_t
> +
> +typedef unsigned short __kernel_ipc_pid_t;
> +#define __kernel_ipc_pid_t __kernel_ipc_pid_t
> +
> +typedef unsigned short __kernel_uid_t;
> +typedef unsigned short __kernel_gid_t;
> +#define __kernel_uid_t __kernel_uid_t
> +
> +typedef unsigned short __kernel_old_dev_t;
> +#define __kernel_old_dev_t __kernel_old_dev_t
> +
> +#include <asm-generic/posix_types.h>

I don't understand why you would want to override any of those.
Changing them unfortunately means rebuilding all of your user
space, but I think it would be better to do that now than to suffer
from this later on.

      Arnd