Re: [Xen-devel] [PATCH v2 01/12] pci: introduce a devfn field to pci_sbdf_t

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 06.06.19 at 11:50, <Paul.Durrant@xxxxxxxxxx> wrote:
>>  -----Original Message-----
>> From: Xen-devel [mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxxx] On Behalf Of 
> Roger Pau Monne
>> Sent: 06 June 2019 10:02
>> To: xen-devel@xxxxxxxxxxxxxxxxxxxx 
>> Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>; Wei Liu <wl@xxxxxxx>; 
>> Konrad 
> Rzeszutek Wilk
>> <konrad.wilk@xxxxxxxxxx>; George Dunlap <George.Dunlap@xxxxxxxxxx>; Andrew 
> Cooper
>> <Andrew.Cooper3@xxxxxxxxxx>; Ian Jackson <Ian.Jackson@xxxxxxxxxx>; Tim 
>> (Xen.org) 
> <tim@xxxxxxx>; Julien
>> Grall <julien.grall@xxxxxxx>; Jan Beulich <jbeulich@xxxxxxxx>; Roger Pau 
>> Monne 
> <roger.pau@xxxxxxxxxx>
>> Subject: [Xen-devel] [PATCH v2 01/12] pci: introduce a devfn field to 
> pci_sbdf_t
>> 
>> This is equivalent to the current extfunc field in term of contents.
>> 
>> Switch the two current users of extfunc to use devfn instead for
>> correctness.
>> 
>> No functional change.
>> 
>> Requested-by: Jan Beulich <jbeulich@xxxxxxxx>
>> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
>> ---
>> Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>> Cc: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>
>> Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
>> Cc: Jan Beulich <jbeulich@xxxxxxxx>
>> Cc: Julien Grall <julien.grall@xxxxxxx>
>> Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
>> Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
>> Cc: Tim Deegan <tim@xxxxxxx>
>> Cc: Wei Liu <wl@xxxxxxx>
>> ---
>> Changes since v1:
>>  - New in this version.
>> ---
>> NB: Paul suggested to name the function field fn instead of func, so
>> that it would match the naming of the devfn field. Sadly the func
>> field cannot be aliased to another field using a union because it's a
>> bit field, so the only option is to rename func to fn.
> 
> Is that true? Can you not do something like...
> 
> union {
>   struct {
>     uint8_t func : 3,
>             dev  : 5;
>   };
>   struct {
>     uint8_t fn   : 3,
>             pad  : 5;

And the "pad" field here wouldn't really be necessary.

Is there a reason "func" needs to be kept? If so, is there a plan to
phase out its use? If so, perhaps fn and dev should be grouped
together, and func should become the (temporary) alias?

Jan


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