linux-kernel - Re: [PATCH] staging: rtl8723bs: Remove ACPI table declaration

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Message-ID: <20180926065909.GA16012@flashbox>
Date:   Tue, 25 Sep 2018 23:59:09 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] staging: rtl8723bs: Remove ACPI table declaration

On Wed, Sep 26, 2018 at 08:49:15AM +0200, Greg Kroah-Hartman wrote:
> On Tue, Sep 25, 2018 at 11:44:37PM -0700, Nathan Chancellor wrote:
> > On Wed, Sep 26, 2018 at 08:22:45AM +0200, Greg Kroah-Hartman wrote:
> > > On Tue, Sep 25, 2018 at 10:39:10PM -0700, Nathan Chancellor wrote:
> > > > Clang warns that the acpi_id declaration is not going to be emitted
> > > > in the final assembly:
> > > > 
> > > > drivers/staging/rtl8723bs/os_dep/sdio_intf.c:25:36: warning: variable
> > > > 'acpi_ids' is not needed and will not be emitted
> > > > [-Wunneeded-internal-declaration]
> > > > static const struct acpi_device_id acpi_ids[] = {
> > > >                                    ^
> > > > 1 warning generated.
> > > > 
> > > > This is because it's marked as static const and it is not used anywhere
> > > > in this file. Doing a git grep on this driver for 'acpi' shows that this
> > > > declaration has been unused since the driver's initial induction. Remove
> > > > it since it's not doing anything.
> > > > 
> > > > Link: https://github.com/ClangBuiltLinux/linux/issues/169
> > > > Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
> > > > ---
> > > >  drivers/staging/rtl8723bs/os_dep/sdio_intf.c | 6 ------
> > > >  1 file changed, 6 deletions(-)
> > > > 
> > > > diff --git a/drivers/staging/rtl8723bs/os_dep/sdio_intf.c b/drivers/staging/rtl8723bs/os_dep/sdio_intf.c
> > > > index 6d02904de63f..d473f9bd08c3 100644
> > > > --- a/drivers/staging/rtl8723bs/os_dep/sdio_intf.c
> > > > +++ b/drivers/staging/rtl8723bs/os_dep/sdio_intf.c
> > > > @@ -22,13 +22,7 @@ static const struct sdio_device_id sdio_ids[] =
> > > >  	{ SDIO_DEVICE(0x024c, 0xb723), },
> > > >  	{ /* end: all zeroes */				},
> > > >  };
> > > > -static const struct acpi_device_id acpi_ids[] = {
> > > > -	{"OBDA8723", 0x0000},
> > > > -	{}
> > > > -};
> > > > -
> > > >  MODULE_DEVICE_TABLE(sdio, sdio_ids);
> > > > -MODULE_DEVICE_TABLE(acpi, acpi_ids);
> > > 
> > > You just removed the ability for the driver to be automatically loaded
> > > if that acpi id is present.
> > > 
> > 
> > I am not sure I understand. Every instance of acpi_device_id that I
> > looked at in the kernel before sending this patch uses MODULE_DEVICE_TABLE
> > but then that acpi_device_id declaration is always used in the driver
> > definition either under the acpi_match_table member or ids member
> > depending on what type of driver it is. Should this one do that as well?
> 
> I don't know, but it's not always necessary.
> 
> > Is that even possible with an sdio driver? I apologize if I am not
> > making sense, I'm not super familiar with these interfaces.
> > 
> > I also read 'Documentation/acpi/enumeration.txt' which makes it seem
> > like the declaration needs to be added to the device definition as well.
> 
> If it is a real acpi driver, yes, you need to actually register it with
> the acpi core.
> 
> But, if it is just using the auto-load functionality of "if this acpi
> string is found, load the module!" then the code is correct as-is.
> 
> Yeah, it's a hack, but does work and helps out for auto-loading drivers
> for "odd" hardware that is not always self-describing.
> 
> thanks,
> 
> greg k-h

Thank you for the explanation, I appreciate that and I'll keep it in
mind should I run across this kind of warning in the future. I'll send a
v2 now that silences this warning through the '__maybe_unused' attribute
like a few other commits that deal with this warning.

Nathan