linux-kernel - Re: [PATCH v8 18/25] powerpc: Implement nvram sync ioctl

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Date:   Sun, 30 Dec 2018 18:25:38 +1100 (AEDT)
From:   Finn Thain <fthain@...egraphics.com.au>
To:     Arnd Bergmann <arnd@...db.de>
cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH v8 18/25] powerpc: Implement nvram sync ioctl

On Sat, 29 Dec 2018, Arnd Bergmann wrote:

> > --- a/drivers/char/nvram.c
> > +++ b/drivers/char/nvram.c
> > @@ -48,6 +48,10 @@
> >  #include <linux/mutex.h>
> >  #include <linux/pagemap.h>
> >
> > +#ifdef CONFIG_PPC
> > +#include <asm/nvram.h>
> > +#include <asm/machdep.h>
> > +#endif
> >
> >  static DEFINE_MUTEX(nvram_mutex);
> >  static DEFINE_SPINLOCK(nvram_state_lock);
> > @@ -331,6 +335,37 @@ static long nvram_misc_ioctl(struct file *file, unsigned int cmd,
> >         long ret = -ENOTTY;
> >
> >         switch (cmd) {
> > +#ifdef CONFIG_PPC
> > +       case OBSOLETE_PMAC_NVRAM_GET_OFFSET:
> > +               pr_warn("nvram: Using obsolete PMAC_NVRAM_GET_OFFSET ioctl\n");
> > +               /* fall through */
> > +       case IOC_NVRAM_GET_OFFSET:
> > +               ret = -EINVAL;
> > +#ifdef CONFIG_PPC_PMAC
> 
> I think it would make be nicer here to keep the ppc bits in arch/ppc,
> and instead add a .ioctl() callback to nvram_ops.
> 

The problem with having an nvram_ops.ioctl() method is the code in the 
!PPC branch. That code would get duplicated because it's needed by both 
X86 and M68K, to implement the checksum ioctls.

> > @@ -369,12 +405,14 @@ static int nvram_misc_open(struct inode *inode, struct file *file)
> >                 return -EBUSY;
> >         }
> >
> > +#ifndef CONFIG_PPC
> >         /* Prevent multiple writers if the set_checksum ioctl is implemented. */
> >         if ((arch_nvram_ops.set_checksum != NULL) &&
> >             (file->f_mode & FMODE_WRITE) && (nvram_open_mode & NVRAM_WRITE)) {
> >                 spin_unlock(&nvram_state_lock);
> >                 return -EBUSY;
> >         }
> > +#endif
> >
> > diff --git a/include/linux/nvram.h b/include/linux/nvram.h
> > index b7bfaec60a43..24a57675dba1 100644
> > --- a/include/linux/nvram.h
> > +++ b/include/linux/nvram.h
> > @@ -18,8 +18,12 @@ struct nvram_ops {
> >         unsigned char   (*read_byte)(int);
> >         void            (*write_byte)(unsigned char, int);
> >         ssize_t         (*get_size)(void);
> > +#ifdef CONFIG_PPC
> > +       long            (*sync)(void);
> > +#else
> >         long            (*set_checksum)(void);
> >         long            (*initialize)(void);
> > +#endif
> >  };
> 
> Maybe just leave all entries visible here, and avoid the above #ifdef checks.
> 

The #ifdef isn't there just to save a few bytes, though it does do that. 
It's really meant to cause a build failure when I mess up somewhere. But 
I'm happy to change it if you can see a reason to do so (?)

-- 

>        Arnd
>