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

From	Andy Shevchenko <andy.shevchenko@gmail.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH] ACPI, APEI: Fixup incorrect 16-bit access width firmware bug
Date	2017-07-26 12:50 +0200
Message-ID	<u7s37-7CE-9@gated-at.bofh.it> (permalink)
References	<u5CJj-37O-11@gated-at.bofh.it> <u5CT0-3b5-23@gated-at.bofh.it> <u7nPQ-56r-13@gated-at.bofh.it>
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On Wed, Jul 26, 2017 at 9:16 AM, Liwei Song <liwei.song@windriver.com> wrote:
> On 07/21/2017 05:56 PM, Andy Shevchenko wrote:
>> On Fri, Jul 21, 2017 at 12:41 PM, Song liwei <liwei.song@windriver.com> wrote:

>>     /* 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;
>>     }

> Thanks for your suggestion, what about the condition like the following?
> The main bug in bios is bit_width is not comfortable with access_bit_width
> So check it first.
>
> if (*access_bit_width < bit_width && bit_offset == 0) {
>         if ((bit_width == 16 && (*paddr & 0x01) == 0) ||
>             (bit_width == 32 && (*paddr & 0x03) == 0) ||
>             (bit_width == 64 && (*paddr & 0x07) == 0))
>                 *access_bit_width = bit_width;
> }

Either works to me.

P.S. Less explicit case is to use bit operations to check those, i.e.
is_power_of_2(), fls().

-- 
With Best Regards,
Andy Shevchenko

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[PATCH] ACPI, APEI: Fixup incorrect 16-bit access width firmware bug Song liwei <liwei.song@windriver.com> - 2017-07-21 11:50 +0200
  Re: [PATCH] ACPI, APEI: Fixup incorrect 16-bit access width firmware bug Andy Shevchenko <andy.shevchenko@gmail.com> - 2017-07-21 12:00 +0200
    Re: [PATCH] ACPI, APEI: Fixup incorrect 16-bit access width firmware  bug Liwei Song <liwei.song@windriver.com> - 2017-07-26 08:20 +0200
      Re: [PATCH] ACPI, APEI: Fixup incorrect 16-bit access width firmware bug Andy Shevchenko <andy.shevchenko@gmail.com> - 2017-07-26 12:50 +0200

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