linux-kernel - Re: [PATCH] ACPI, APEI: Fixup incorrect 16-bit access width firmware bug

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Date:   Fri, 21 Jul 2017 12:56:17 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Song liwei <liwei.song@...driver.com>
Cc:     "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>,
        linux-acpi <linux-acpi@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ACPI, APEI: Fixup incorrect 16-bit access width firmware bug

On Fri, Jul 21, 2017 at 12:41 PM, Song liwei <liwei.song@...driver.com> wrote:

> [Firmware Bug]: APEI: Invalid bit width + offset in GAR [0xb2/16/0/1/1]
>
> This is due to an 8-bit access width is specified for a 16-bit register,
> Do bit_width check just like what the original commit have done.

>         else if (bit_width == 64 && bit_offset == 0 && (*paddr & 0x07) == 0 &&
>             *access_bit_width < 64)
>                 *access_bit_width = 64;
> +       else if (bit_width == 16 && bit_offset == 0 && (*paddr & 0x01) == 0 &&
> +           *access_bit_width < 16)
> +               *access_bit_width = 16;

Wouldn't be better to rearrange that it will go in a sequence
(16,32,64 or 64,32,16) ?

or move bit_offset == 0 into external condion

    /* Fixup common BIOS bug */
    if (bit_offset == 0) {
      if (bit_width == 16 && (*paddr & 0x01) == 0 && *access_bit_width < 16)
               *access_bit_width = 16;
      else if (bit_width == 32 && (*paddr & 0x03) == 0 &&
*access_bit_width < 32)
               *access_bit_width = 32;
      else if (bit_width == 64 && (*paddr & 0x07) == 0 &&
*access_bit_width < 64)
               *access_bit_width = 64;
    }


It might be (I'm not sure it will make it better, just a side note)
considered to convert each internal conditional to

...if (bit_width == XX && (*paddr & YY) == 0)
               *access_bit_width = max(*access_bit_width, bit_width);

-- 
With Best Regards,
Andy Shevchenko