linux-kernel - Re: [PATCH v5 4/9] drivers: base cacheinfo: Add support for ACPI based firmware tables

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Date:   Wed, 13 Dec 2017 00:41:07 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Jeremy Linton <jeremy.linton@....com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Sudeep Holla <sudeep.holla@....com>,
        Hanjun Guo <hanjun.guo@...aro.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Will Deacon <will.deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Mark Rutland <mark.rutland@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>, jhugo@...eaurora.org,
        wangxiongfeng2@...wei.com, Jonathan.Zhang@...ium.com,
        Al Stone <ahs3@...hat.com>, Jayachandran.Nair@...ium.com,
        austinwc@...eaurora.org, Len Brown <lenb@...nel.org>
Subject: Re: [PATCH v5 4/9] drivers: base cacheinfo: Add support for ACPI
 based firmware tables

On Wed, Dec 13, 2017 at 12:37 AM, Jeremy Linton <jeremy.linton@....com> wrote:
> On 12/12/2017 05:02 PM, Rafael J. Wysocki wrote:
>>
>> On Tue, Dec 12, 2017 at 11:55 PM, Jeremy Linton <jeremy.linton@....com>
>> wrote:
>>>
>>> Hi,
>>>
>>>
>>> On 12/12/2017 11:25 AM, Rafael J. Wysocki wrote:
>>>>
>>>>
>>
>> [cut]
>
>
> (trimming list)
>
>
>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> What about converting this to using struct fwnode instead of adding
>>>>>> fields to it?
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> I didn't really want to add another field here, but I've also pointed
>>>>> out
>>>>> how I thought converting it to a fwnode wasn't a good choice.
>>>>>
>>>>> https://lkml.org/lkml/2017/11/20/502
>>>>>
>>>>> Mostly because IMHO its even more misleading (lacking any
>>>>> fwnode_operations)
>>>>> than misusing the of_node as a void *.
>>>>
>>>>
>>>>
>>>> I'm not sure what you mean.
>>>
>>>
>>>
>>> Converting the DT drivers/cacheinfo.c code to use a fwnode_handle is
>>> straightforward. But IMHO it doesn't solve the readability problem of
>>> either
>>> casting the ACPI/PPTT token directly to the resulting fwnode_handle *, or
>>> alternatively an actual fwnode_handle with bogus fwnode_operations to
>>> wrap
>>> that token.
>>
>>
>> I'm not talking about that at all.
>>
>>>>
>>>> Anyway, the idea is to have one pointer in there instead of two that
>>>> cannot be used at the same time and there's no reason why of_node
>>>> should be special.
>>>
>>>
>>>
>>>          Avoid two pointers for size, or readability? Because the last
>>> version had a union with of_node, which isn't strictly necessary as I can
>>> just cast the pptt token to of_node. There is exactly one line of code
>>> after
>>> that which uses the token and it doesn't care about type.
>>
>>
>> So call this field "token" or similar.  Don't call it "of_node" and
>> don't introduce another "firmware_node" thing in addition to that.
>> That just is a mess, sorry.
>
>
> I sort of agree, I think I can just change the whole of_node to a generic
> 'void *firmware_unique' which works fine for the PPTT code, it should also
> work for the DT code in cache_leaves_are_shared().
>
> The slight gocha is there is a bit of DT code which initially runs earlier
> that uses of_node as an indirect parameter to a couple functions (by just
> passing the cacheinfo). Let me see if I can tweak that a bit.
>
> Frankly, If I understood completely all the *priv cases I suspect it might
> be possible to collapse *of_node into that as well. That is as long as no
> one decides to flush out DT on x86, or PPTT on x86.

I'm not aware of any plans to go in that direction.

Anyway, that would be a worry of whoever wanted to do that.  No need
to worry about it upfront.