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

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Message-Id: <201407180931.32502.linux@rainbow-software.org>
Date:	Fri, 18 Jul 2014 09:31:32 +0200
From:	Ondrej Zary <linux@...nbow-software.org>
To:	matwey@....msu.ru
Cc:	gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
	linux-parport@...ts.infradead.org, hsommer@....org,
	gnomes@...rguk.ukuu.org.uk, matwey.kornilov@...il.com
Subject: Re: [PATCHv4 2/2] parport: parport_pc: Implement CPU model check to cut off false-positives

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
--
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