Re: [PATCH v2] hpet: Fix missing '=' character in the __setup() code of hpet_mmap_enable

[Buland Singh]

On 12/20/18 5:59 PM, Greg KH wrote:
> On Thu, Dec 20, 2018 at 05:35:24PM +0530, Buland Singh wrote:
> > Commit '3d035f580699 ("drivers/char/hpet.c: allow user controlled mmap for
> > user processes")' introduced a new kernel command line parameter hpet_mmap,
> > that is required to expose the memory map of the HPET registers to
> > user-space. Unfortunately the kernel command line parameter 'hpet_mmap' is
> > broken and never takes effect due to missing '=' character in the __setup()
> > code of hpet_mmap_enable.
> >
> > Before this patch:
> >
> > dmesg output with the kernel command line parameter hpet_mmap=1
> >
> > [    0.204152] HPET mmap disabled
> >
> > dmesg output with the kernel command line parameter hpet_mmap=0
> >
> > [    0.204192] HPET mmap disabled
> >
> > After this patch:
> >
> > dmesg output with the kernel command line parameter hpet_mmap=1
> >
> > [    0.203945] HPET mmap enabled
> >
> > dmesg output with the kernel command line parameter hpet_mmap=0
> >
> > [    0.204652] HPET mmap disabled
> >
> > Fixes: 3d035f580699 ("drivers/char/hpet.c: allow user controlled mmap for user processes")
> > Signed-off-by: Buland Singh <bsingh@xxxxxxxxxx>
> > ---
> >   drivers/char/hpet.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/char/hpet.c b/drivers/char/hpet.c
> > index 4a22b4b41aef..9bffcd37cc7b 100644
> > --- a/drivers/char/hpet.c
> > +++ b/drivers/char/hpet.c
> > @@ -377,7 +377,7 @@ static __init int hpet_mmap_enable(char *str)
> >   	pr_info("HPET mmap %s\n", hpet_mmap_enabled ? "enabled" : "disabled");
> >   	return 1;
> >   }
> > -__setup("hpet_mmap", hpet_mmap_enable);
> > +__setup("hpet_mmap=", hpet_mmap_enable);

Hello Greag,

> This has _never_ worked?  Since 3.13?  

Yes, that's true :)

> Why not just remove the thing as it is obvious no one actually has ever used it.  > That would make the code even simpler :)

Data Plane Development Kit (DPDK)[1] provides API that requires the CONFIG_HPET_MMAP
kernel configuration option to be enabled[2]. Some end users might want to use the
HPET MMAP functionality within the application.
 
Regards,
Buland Singh

[1] https://www.dpdk.org
[2] https://doc.dpdk.org/guides-18.08/linux_gsg/enable_func.html