linux-kernel - Re: [RFC 1/6] powerpc:/drc Define interface to acquire arch-specific drc info

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Date:   Tue, 29 Jan 2019 10:21:09 -0600
From:   Michael Bringmann <mwb@...ux.vnet.ibm.com>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Tyrel Datwyler <turtle.in.the.kernel@...il.com>,
        "open list:LINUX FOR POWERPC (32-BIT AND 64-BIT)" 
        <linuxppc-dev@...ts.ozlabs.org>, linux-kernel@...r.kernel.org
Cc:     Juliet Kim <minkim@...ibm.com>,
        Thomas Falcon <tlfalcon@...ux.vnet.ibm.com>,
        Tyrel Datwyler <tyreld@...ux.vnet.ibm.com>,
        nathanl@...ux.vnet.ibm.com
Subject: Re: [RFC 1/6] powerpc:/drc Define interface to acquire arch-specific
 drc info

On 1/29/19 3:31 AM, Michael Ellerman wrote:
> Tyrel Datwyler <turtle.in.the.kernel@...il.com> writes:
>> On 12/14/2018 12:50 PM, Michael Bringmann wrote:
>>> Define interface to acquire arch-specific drc info to match against
>>> hotpluggable devices.  The current implementation exposes several
>>> pseries-specific dynamic memory properties in generic kernel code.
>>> This patch set provides an interface to pull that code out of the
>>> generic kernel.
>>>
>>> Signed-off-by: Michael Bringmann <mwb@...ux.vnet.ibm.com>
>>> ---
>>>  include/linux/topology.h |    9 +++++++++
>>>  1 file changed, 9 insertions(+)
>>>
>>> diff --git a/include/linux/topology.h b/include/linux/topology.h
>>> index cb0775e..df97f5f 100644
>>> --- a/include/linux/topology.h
>>> +++ b/include/linux/topology.h
>>> @@ -44,6 +44,15 @@
>>
>> As far as I know pseries is the only platform that uses DR connectors, and I
>> highly doubt that any other powerpc platform or arch ever will. So, I'm not sure
>> that this is really generic enough to belong in topology.h.
> 
> Right. This does not belong in include/linux.
> 
>> If anything I would
>> suggest putting this in an include in arch/powerpc/include/ named something like
>> drcinfo.h or pseries-drc.h. That will make it visible to modules like rpaphp
>> that want/need to use this functionality.
> 
> Yeah that would make more sense.

If you see no objection to referencing a powerpc-specific function from
the code ...

> 
> Using "arch" in the name is wrong, it's pseries specific so
> pseries_find_drc_match() would be more appropriate.
> 
>>> +int arch_find_drc_match(struct device_node *dn,
>>> +			bool (*usercb)(struct device_node *dn,
>>> +				u32 drc_index, char *drc_name,
>>> +				char *drc_type, u32 drc_power_domain,
>>> +				void *data),
>>> +			char *opt_drc_type, char *opt_drc_name,
>>> +			bool match_drc_index, bool ck_php_type,
>>> +			void *data);
> 
> This function signature is kind of insane.
> 
> You end with calls like:
> 
> +	return arch_find_drc_match(dn, rpaphp_add_slot_cb,
> +			NULL, NULL, false, true, NULL);
> 
> Which is impossible to parse.
> 
> I feel like maybe this isn't the right level of abstraction.

...
I had already been considering simplifying the interface for these
calls to something like the following:

int rpaphp_check_drc_props(struct device_node *dn, char *drc_name,
			char *drc_type)
{
    return pseries_find_drc_match(dn, drc_type, drc_name);
}
...
int rpaphp_add_slot(struct device_node *dn)
{
       if (!dn->name || strcmp(dn->name, "pci"))
               return 0;

       return pseries_add_drc_slot(dn, rpaphp_add_slot_cb);
}
...

Further details would be hidden within the pseries code.


> 
> cheers

Regards

-- 
Michael W. Bringmann
Linux Technology Center
IBM Corporation
Tie-Line  363-5196
External: (512) 286-5196
Cell:       (512) 466-0650
mwb@...ux.vnet.ibm.com