linux-kernel - Re: [PATCH v3] dcdbas: Add support for WSMT ACPI table

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Date:   Thu, 14 Jun 2018 09:22:57 -0500
From:   Stuart Hayes <stuart.w.hayes@...il.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Darren Hart <dvhart@...radead.org>, Douglas_Warzecha@...l.com,
        Mario Limonciello <mario.limonciello@...l.com>,
        Jared.Dominguez@...l.com,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Platform Driver <platform-driver-x86@...r.kernel.org>
Subject: Re: [PATCH v3] dcdbas: Add support for WSMT ACPI table

On 6/13/2018 3:54 AM, Andy Shevchenko wrote:
>> +               /* Calling Interface SMI
> 
> I suppose the style of the comments like
> /*
>  * Calling ...
> ...

Yes... goof on my part.  Thanks.

>> +                *
>> +                * Provide physical address of command buffer field within
>> +                * the struct smi_cmd... can't use virt_to_phys on smi_cmd
>> +                * because address may be from memremap.
> 
> Wait, memremap() might return a virtual address. How we be sure that
> we got still physical address here?
> 
> (Also note () when referring to functions)
>
>> +                */
>> +               smi_cmd->ebx = smi_data_buf_phys_addr +
>> +                               offsetof(struct smi_cmd, command_buffer);
> 
> Btw, can it be one line (~83 character are okay for my opinion).
> 

Before this patch, the address in smi_cmd always came from an alloc, so
virt_to_phys() was used to get the physical address here.  With WSMT, we
could be using a BIOS-provided buffer for SMI, in which case the address in
smi_cmd will come from memremap(), so we can't use virt_to_phys() on it.
So instead I changed this to use the physical address of smi_data_buf that
is stored in smi_data_buf_phys_addr, which will be valid regardless of how
the address of smi_data_buf was generated.

But that would be like 97 characters long if I made it all one line...

>> +       acpi_get_table(ACPI_SIG_WSMT, 0, (struct acpi_table_header **)&wsmt);
>> +       if (!wsmt)
>> +               return 0;
>> +
>> +       /* Check if WSMT ACPI table shows that protection is enabled */
>> +       if (!(wsmt->protection_flags & ACPI_WSMT_FIXED_COMM_BUFFERS)
> 
>> +           || !(wsmt->protection_flags
>> +                & ACPI_WSMT_COMM_BUFFER_NESTED_PTR_PROTECTION))
> 
> Better to indent like
> 
> if (... ||
>  !(... & ...)
> 

Yes thanks.

>> +               return 0;
>> +
>> +       /* Scan for EPS (entry point structure) */
>> +       for (addr = (u8 *)__va(0xf0000);
>> +            addr < (u8 *)__va(0x100000 - sizeof(struct smm_eps_table));
> 
>> +            addr += 1) {
> 
> This wasn't commented IIRC and changed. So, why?
> 

I changed this is response to your earlier comment (7 june)... you had pointed
out that it would be better if I put an "if (eps) break;" inside the for loop
instead of having "&& !eps" in the condition of the for loop.  I put the note
"Changed loop searching 0xf0000 to be more readable" in the list of changes for
patch version v3 to cover this change.

Thanks again for your time!