On 10 November 2014 08:39, Jassi Brar <jaswinder.singh@xxxxxxxxxx> wrote: > On 10 November 2014 18:27, Ashwin Chaugule <ashwin.chaugule@xxxxxxxxxx> wrote: >> On 9 November 2014 23:13, Jassi Brar <jaswinder.singh@xxxxxxxxxx> wrote: >>> >>>>>> based on the discussions that followed since, we decided that its best >>>>>> to add a separate PCC lookup and registration API. The main reason >>>>>> being, we dont have a way to list all mbox providers in ACPI in a way >>>>>> that DT does. e.g. in DT, the client->dev is used to look up mbox >>>>>> controllers. In ACPI, a client cant specify which mbox controllers to >>>>>> associate with, if it can attach to multiple. With the PCC specific >>>>>> API, if the client calls it, the controller knows where to look, >>>>>> because that lookup is PCC specific. >>>>>> >>>>>> In your patch, the assumption that PCC is the only ACPI mbox provider, >>>>>> maybe true today, but that can change anytime. >>>>>> >>>>> Please read my patch again, we can have ACPI as well as DT populated >>>>> clients. All that you intend to do with this patch can be done there >>>>> and _without_ adding new apis. >>>> >>>> Read it again. Not arguing that your patch wont work for DT and ACPI, >>>> but your assumption that ACPI supports PCC as the only mbox >>>> controller, may not hold true. The global_xlate function will work >>>> fine for PCC, but may not work for other ACPI (non-DT) mbox >>>> controllers. Using the signature field/index byte works only for PCC. >>>> We've already been through this discussion with Mark and Arnd and we >>>> came up with the PCC API. >>>> >>> Please read it yet again. There is no assumption that PCC is the only >>> mbox in ACPI (though I think that is very likely). The function and >>> its argument are both named _global_. 'Signature' is mentioned only as >>> an example in case of PCC. The PCC controller driver could expect the >>> global_id to be 'signature' of the subspace, similarly another non-DT >>> mailbox controller driver will expect its own different 'signature' >>> (say 0xdead0000 | id_16bits). In the patch I submitted we try >>> .global_xlate() of all such mboxes and only one, which finds its >>> id-space specified, will return a channel. >>> >>> Ideally, global-id space isn't very clean, but for mailbox we anyway >>> have to have a direct understanding between controller and client >>> drivers. So having global IDs is a great tradeoff if we avoid messing >>> up the api. >> >> How is this different than expecting the client to pass a string name >> of the mbox controller it wants? >> > Global-ID is ugly, string matching is uglier. String matching requires > changes to client and provider structures as opposed to simple > numerical comparison to find a suitable channel. And both have the problem that we cant guarantee uniqueness [1][2]. Having a separate API solves this problem. Ashwin [1] - http://www.spinics.net/lists/linux-acpi/msg52271.html [2] - http://www.spinics.net/lists/linux-acpi/msg52377.html -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
