linux-kernel - Re: [PATCH v2] hpet: Fix missing '=' character in the __setup() code of hpet_mmap

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Date:   Thu, 20 Dec 2018 15:09:51 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Buland Singh <bsingh@...hat.com>
Cc:     clemens@...isch.de, arnd@...db.de, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH v2] hpet: Fix missing '=' character in the __setup() code
 of hpet_mmap_enable

On Thu, Dec 20, 2018 at 07:12:55PM +0530, Buland Singh wrote:
> 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@...hat.com>
> > > ---
> > >   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.

But, obviously, they really don't need to do that from the kernel
command line as no one has ever noticed this didn't work :)

Also, that page:

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

Does not say to use this command line option either.  So if no one has
ever used it, please, let us just delete it.

thanks,

greg k-h