linux-kernel - Re: [PATCH v8 20/25] powerpc, fbdev: Use arch_nvram_ops methods instead of nvram_read_byte() and nvram_write

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Date:   Sun, 30 Dec 2018 10:43:33 +1100 (AEDT)
From:   Finn Thain <fthain@...egraphics.com.au>
To:     LEROY Christophe <christophe.leroy@....fr>
cc:     linux-fbdev@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-m68k@...ts.linux-m68k.org,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Paul Mackerras <paulus@...ba.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v8 20/25] powerpc, fbdev: Use arch_nvram_ops methods
 instead of nvram_read_byte() and nvram_write_byte()

On Sat, 29 Dec 2018, LEROY Christophe wrote:

> Finn Thain <fthain@...egraphics.com.au> a ?crit?:
> 
> > Make use of arch_nvram_ops in device drivers so that the nvram_* function
> > exports can be removed.
> > 
> > Since they are no longer global symbols, rename the PPC32 nvram_* functions
> > appropriately.
> > 
> > Signed-off-by: Finn Thain <fthain@...egraphics.com.au>
> > ---
> > arch/powerpc/kernel/setup_32.c             | 8 ++++----
> > drivers/char/generic_nvram.c               | 4 ++--
> > drivers/video/fbdev/controlfb.c            | 4 ++--
> > drivers/video/fbdev/imsttfb.c              | 4 ++--
> > drivers/video/fbdev/matrox/matroxfb_base.c | 2 +-
> > drivers/video/fbdev/platinumfb.c           | 4 ++--
> > drivers/video/fbdev/valkyriefb.c           | 4 ++--
> > 7 files changed, 15 insertions(+), 15 deletions(-)
> > 
> > diff --git a/arch/powerpc/kernel/setup_32.c b/arch/powerpc/kernel/setup_32.c
> > index e0d045677472..bdbe6acbef11 100644
> > --- a/arch/powerpc/kernel/setup_32.c
> > +++ b/arch/powerpc/kernel/setup_32.c
> > @@ -152,20 +152,18 @@ __setup("l3cr=", ppc_setup_l3cr);
> > 
> > #ifdef CONFIG_GENERIC_NVRAM
> > 
> > -unsigned char nvram_read_byte(int addr)
> > +static unsigned char ppc_nvram_read_byte(int addr)
> > {
> > 	if (ppc_md.nvram_read_val)
> > 		return ppc_md.nvram_read_val(addr);
> > 	return 0xff;
> > }
> > -EXPORT_SYMBOL(nvram_read_byte);
> > 
> > -void nvram_write_byte(unsigned char val, int addr)
> > +static void ppc_nvram_write_byte(unsigned char val, int addr)
> > {
> > 	if (ppc_md.nvram_write_val)
> > 		ppc_md.nvram_write_val(addr, val);
> > }
> > -EXPORT_SYMBOL(nvram_write_byte);
> > 
> > static ssize_t ppc_nvram_get_size(void)
> > {
> > @@ -182,6 +180,8 @@ static long ppc_nvram_sync(void)
> > }
> > 
> > const struct nvram_ops arch_nvram_ops = {
> > +	.read_byte      = ppc_nvram_read_byte,
> > +	.write_byte     = ppc_nvram_write_byte,
> > 	.get_size       = ppc_nvram_get_size,
> > 	.sync           = ppc_nvram_sync,
> > };
> > diff --git a/drivers/char/generic_nvram.c b/drivers/char/generic_nvram.c
> > index f32d5663de95..41b76bf9614e 100644
> > --- a/drivers/char/generic_nvram.c
> > +++ b/drivers/char/generic_nvram.c
> > @@ -48,7 +48,7 @@ static ssize_t read_nvram(struct file *file, char __user
> > *buf,
> > 	if (*ppos >= nvram_len)
> > 		return 0;
> > 	for (i = *ppos; count > 0 && i < nvram_len; ++i, ++p, --count)
> > -		if (__put_user(nvram_read_byte(i), p))
> > +		if (__put_user(arch_nvram_ops.read_byte(i), p))
> 
> Instead of modifying all drivers (in this patch and previous ones related to
> other arches), wouldn't it be better to add helpers like the following in
> nvram.h:
> 
> Static inline unsigned char nvram_read_byte(int addr)
> {
>        return arch_nvram_ops.read_byte(addr);
> }
> 

Is there some benefit, or is that just personal taste?

Avoiding changes to call sites avoids code review, but I think 1) the 
thinkpad_acpi changes have already been reviewed and 2) the fbdev changes 
need review anyway.

Your suggesion would add several new entities and one extra layer of 
indirection.

I think indirection harms readability because now the reader now has to go 
and look up the meaning of the new entities.

It's not the case that we need to choose between definitions of 
nvram_read_byte() at compile time, or stub them out:

#ifdef CONFIG_FOO
static inline unsigned char nvram_read_byte(int addr)
{
	return arch_nvram_ops.read_byte(addr);
}
#else
static inline unsigned char nvram_read_byte(int addr) { }
#endif

And I don't anticipate a need for a macro here either:

#define nvram_read_byte(a) random_nvram_read_byte_impl(a)

I think I've used the simplest solution.

-- 

> Christophe
>