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

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Date:   Mon, 21 Aug 2017 22:21:40 +0000
From:   "Kani, Toshimitsu" <toshi.kani@....com>
To:     "rafael@...nel.org" <rafael@...nel.org>
CC:     "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 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.

Thanks,
-Toshi