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

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Message-ID: <fdb60100-3973-b9e3-487a-882836f8751e@arm.com>
Date:   Tue, 12 Dec 2017 17:37:48 -0600
From:   Jeremy Linton <jeremy.linton@....com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     "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 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.