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 19:12:55 +0530
From:   Buland Singh <bsingh@...hat.com>
To:     Greg KH <gregkh@...uxfoundation.org>
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 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.
  
Regards,
Buland Singh

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