linux-kernel - Re: [PATCHv4 2/2] parport: parport_pc: Implement CPU model check to cut off false-positives

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Message-ID: <CAJs94Ebr_39U4EEQYweuZvXeC0sMdrr7D1EPNae0ujFNTeLq8w@mail.gmail.com>
Date:	Wed, 13 Aug 2014 12:04:55 +0400
From:	"Matwey V. Kornilov" <matwey@....msu.ru>
To:	Ondrej Zary <linux@...nbow-software.org>
Cc:	Greg KH <gregkh@...uxfoundation.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-parport <linux-parport@...ts.infradead.org>,
	Heiko Andreas Sommer <hsommer@....org>,
	gnomes@...rguk.ukuu.org.uk
Subject: Re: [PATCHv4 2/2] parport: parport_pc: Implement CPU model check to
 cut off false-positives

Hi,

What do you think, would it be better just to left the check for all
x86 32-bit hardware?.


2014-07-18 11:31 GMT+04:00 Ondrej Zary <linux@...nbow-software.org>:
> On Friday 18 July 2014, matwey@....msu.ru wrote:
>> From: "Matwey V. Kornilov" <matwey@....msu.ru>
>>
>> The code in intel_bug_present is known to produce much false-positives.
>> It is believed that the affected by the bug hardware are used with either
>> Intel 80486 or Pentium.
>>
>> Perform the check only when the kernel configured as CONFIG_X86_32,
>> then use cpuinfo_x86 of the first available CPU to check the model
>> and run initial check code.
>>
>> Suggested-by: One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
>> Tested-by: Heiko Andreas Sommer <hsommer@....org>
>> Signed-off-by: Matwey V. Kornilov <matwey@....msu.ru>
>> ---
>>  drivers/parport/parport_pc.c | 21 ++++++++++++++++++++-
>>  1 file changed, 20 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/parport/parport_pc.c b/drivers/parport/parport_pc.c
>> index a6eaafb..6b28f9f 100644
>> --- a/drivers/parport/parport_pc.c
>> +++ b/drivers/parport/parport_pc.c
>> @@ -65,6 +65,7 @@
>>  #include <linux/parport_pc.h>
>>  #include <linux/via.h>
>>  #include <asm/parport.h>
>> +#include <asm/processor.h>
>>
>>  #define PARPORT_PC_MAX_PORTS PARPORT_MAX
>>
>> @@ -1702,7 +1703,11 @@ static int parport_ECP_supported(struct parport *pb)
>>  }
>>  #endif
>>
>> -static int intel_bug_present(struct parport *pb)
>> +/*  It is believed that CPU model correlates with buggy LPT chipset model.
>> +    Here we check that or CPU is elder than Pentium Pro: either 80486 or
>> Pentium. +    If it is then we perform The Check. */
>> +#ifdef CONFIG_X86_32
>> +static int intel_bug_present_check_epp(struct parport *pb)
>>  {
>>       const struct parport_pc_private *priv = pb->private_data;
>>       int bug_present = 0;
>> @@ -1725,6 +1730,20 @@ static int intel_bug_present(struct parport *pb)
>>
>>       return bug_present;
>>  }
>> +static int intel_bug_present(struct parport *pb)
>> +{
>> +     struct cpuinfo_x86 *c = &cpu_data(0);
>> +
>> +     if (c->x86_vendor == X86_VENDOR_INTEL && (c->x86 == 4 || c->x86 == 5))
>> +             return intel_bug_present_check_epp(pb);
>
> You can have a non-Intel CPU in a 486 or Pentium board.
>
>> +     return 0;
>> +}
>> +#else
>> +static int intel_bug_present(struct parport *pb)
>> +{
>> +     return 0;
>> +}
>> +#endif
>>
>>  static int parport_ECPPS2_supported(struct parport *pb)
>>  {
>
>
>
> --
> Ondrej Zary



-- 
With best regards,
Matwey V. Kornilov.
Sternberg Astronomical Institute, Lomonosov Moscow State University, Russia
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