linux-kernel - Re: [PATCH v3 1/5] ACPI / blacklist: add acpi_match_platform

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Date:   Tue, 22 Aug 2017 00:26:51 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     "Kani, Toshimitsu" <toshi.kani@....com>
Cc:     "rafael@...nel.org" <rafael@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "mchehab@...nel.org" <mchehab@...nel.org>,
        "rjw@...ysocki.net" <rjw@...ysocki.net>,
        "bp@...en8.de" <bp@...en8.de>,
        "tony.luck@...el.com" <tony.luck@...el.com>,
        "lenb@...nel.org" <lenb@...nel.org>,
        "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
        "linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>
Subject: Re: [PATCH v3 1/5] ACPI / blacklist: add acpi_match_platform_list()

On Tue, Aug 22, 2017 at 12:21 AM, Kani, Toshimitsu <toshi.kani@....com> wrote:
> On Mon, 2017-08-21 at 23:49 +0200, Rafael J. Wysocki wrote:
>> On Mon, Aug 21, 2017 at 11:06 PM, Kani, Toshimitsu <toshi.kani@....co
>> m> wrote:
>> > On Mon, 2017-08-21 at 22:31 +0200, Rafael J. Wysocki wrote:
>> > > On Mon, Aug 21, 2017 at 7:36 PM, Borislav Petkov <bp@...en8.de>
>> > > wrote:
>> > > > On Mon, Aug 21, 2017 at 05:23:37PM +0000, Kani, Toshimitsu
>> > > > wrote:
>> > > > > > > 'data' here is private to the caller.  So, I do not think
>> > > > > > > we need to define the bits.  Shall I change the name to
>> > > > > > > 'driver_data' to make it more explicit?
>> > > > > >
>> > > > > > You changed it to 'data'. It was a u32-used-as-boolean
>> > > > > > is_critical_error before.
>> > > > > >
>> > > > > > So you can just as well make it into flags and people can
>> > > > > > extend those flags if needed. A flag bit should be enough
>> > > > > > in most cases anyway. If they really need driver_data, then
>> > > > > > they can add a void *member.
>> > > > >
>> > > > > Hmm.. In patch 2, intel_pstate_platform_pwr_mgmt_exists()
>> > > > > uses this field for PSS and PCC, which are enum values.  I
>> > > > > think we should allow drivers to set any values here.  I
>> > > > > agree that it may need to be void * if we also allow drivers
>> > > > > to set a pointer here.
>> > > >
>> > > > Let's see what Rafael prefers.
>> > >
>> > > I would retain the is_critical_error field and use that for
>> > > printing the recoverable / non-recoverable message.  This is kind
>> > > of orthogonal to whether or not any extra data is needed and that
>> > > can be an additional field.  In that case unsigned long should be
>> > > sufficient to accommodate a pointer if need be.
>> >
>> > Yes, we will retain the field.  The question is whether this field
>> > should be retained as a driver's private data or ACPI-managed
>> > flags.
>>
>> Thanks for the clarification.
>>
>> > My patch implements the former, which lets the callers to define
>> > the data values.  For instance, acpi_blacklisted() uses this field
>> > as is_critical_error value, and
>> > intel_pstate_platform_pwr_mgmt_exists() uses it as oem_pwr_table
>> > value.
>> >
>> > Boris suggested the latter, which lets ACPI to define the flags,
>> > which are then used by the callers.  For instance, he suggested
>> > ACPI to define bit0 as is_critical_error.
>> >
>> > #define ACPI_PLAT_IS_CRITICAL_ERROR     BIT(0)
>>
>> So my point is that we can have both the ACPI-managed flags and the
>> the caller-defined data at the same time as separate items.
>>
>> That would allow of maximum flexibility IMO.
>
> I agree in general.  Driver private data allows flexibility to drivers
> when the values are driver-private.  ACPI-managed flags allows ACPI to
> control the interfaces based on the flags.
>
> Since we do not have use-case of the latter case yet, i.e.
> acpi_match_platform_list() does not need to check the flags, I'd
> suggest that we keep 'data' as driver-private.  We can add 'flags' as a
> separate member to the structure when we find the latter use-case.

OK

Thanks,
Rafael