Re: [PATCH v3] mailbox: pcc: Support HW-Reduced Communication Subspace type 2

[Hoan Tran]

On Tue, Aug 16, 2016 at 4:56 AM, Rafael J. Wysocki <rjw@xxxxxxxxxxxxx> wrote:
> On Monday, August 15, 2016 04:41:22 PM Hoan Tran wrote:
>> Hi Rafael,
>>
>> On Mon, Aug 15, 2016 at 4:18 PM, Rafael J. Wysocki <rjw@xxxxxxxxxxxxx> wrote:
>> > On Monday, August 15, 2016 09:45:24 AM Hoan Tran wrote:
>> >> On Mon, Jun 27, 2016 at 2:32 PM, Rafael J. Wysocki <rjw@xxxxxxxxxxxxx> wrote:
>> >> >
>> >> > On Monday, June 27, 2016 11:27:42 AM Hoan Tran wrote:
>> >> > > Hi Jassi and Rafael,
>> >> > >
>> >> > > On Wed, Jun 15, 2016 at 9:19 AM, Prakash, Prashanth
>> >> > > <pprakash@xxxxxxxxxxxxxx> wrote:
>> >> > > >
>> >> > > >
>> >> > > > On 6/9/2016 4:43 PM, Hoan Tran wrote:
>> >> > > >> Hi Prashanth,
>> >> > > >>
>> >> > > >> On Thu, Jun 9, 2016 at 3:25 PM, Prakash, Prashanth
>> >> > > >> <pprakash@xxxxxxxxxxxxxx> wrote:
>> >> > > >>>
>> >> > > >>> On 6/9/2016 2:47 PM, Hoan Tran wrote:
>> >> > > >>>> Hi Ashwin and Prashanth,
>> >> > > >>>>
>> >> > > >>>> On Wed, Jun 8, 2016 at 5:41 PM, Hoan Tran <hotran@xxxxxxx> wrote:
>> >> > > >>>>> Hi Prashanth,
>> >> > > >>>>>
>> >> > > >>>>>
>> >> > > >>>>> On Wed, Jun 8, 2016 at 5:32 PM, Prakash, Prashanth
>> >> > > >>>>> <pprakash@xxxxxxxxxxxxxx> wrote:
>> >> > > >>>>>> On 6/8/2016 10:24 AM, Hoan Tran wrote:
>> >> > > >>>>>>> Hi Ashwin,
>> >> > > >>>>>>>
>> >> > > >>>>>>> On Wed, Jun 8, 2016 at 5:18 AM, Ashwin Chaugule
>> >> > > >>>>>>> <ashwin.chaugule@xxxxxxxxxx> wrote:
>> >> > > >>>>>>>> + Prashanth (Can you please have a look as well?)
>> >> > > >>>>>>>>
>> >> > > >>>>>>>> On 31 May 2016 at 15:35, Hoan Tran <hotran@xxxxxxx> wrote:
>> >> > > >>>>>>>>> Hi Ashwin,
>> >> > > >>>>>>>> Hi,
>> >> > > >>>>>>>>
>> >> > > >>>>>>>> Sorry about the delay. I'm in the middle of switching jobs and
>> >> > > >>>>>>>> locations, so its been a bit crazy lately.
>> >> > > >>>>>>> It's ok and hope you're doing well.
>> >> > > >>>>>>>
>> >> > > >>>>>>>> I dont have any major
>> >> > > >>>>>>>> concerns with this code, although there could be subtle issues with
>> >> > > >>>>>>>> this IRQ thing. In this patchset, your intent is to add support for
>> >> > > >>>>>>>> PCC subspace type 2. But you're also adding support for tx command
>> >> > > >>>>>>>> completion which is not specific to Type 2. We could support that even
>> >> > > >>>>>>>> in Type 1. Hence I wanted to separate the two, not just for review,
>> >> > > >>>>>>>> but also the async IRQ completion has subtle issues esp. in the case
>> >> > > >>>>>>>> of async platform notification, where you could have a PCC client in
>> >> > > >>>>>>>> the OS writing to the cmd bit and the platform sending an async
>> >> > > >>>>>>>> notification by writing to some bits in the same 8byte address as the
>> >> > > >>>>>>>> cmd bit. So we need some mutual exclusivity there, otherwise the OS
>> >> > > >>>>>>>> and platform could step on each other. Perhaps Prashanth has better
>> >> > > >>>>>>>> insight into this.
>> >> > > >>>>>>> I think, this mutual exclusivity could be in another patch.
>> >> > > >>>>>> Ashwin,
>> >> > > >>>>>> Sorry, I am not sure how we can prevent platform and OSPM from stepping on
>> >> > > >>>>>> each other.  There is a line is spec that says "all operations on status field
>> >> > > >>>>>> must be made using interlocked operations", but not sure what these
>> >> > > >>>>>> interlocked operation translates to.
>> >> > > >>>>> Yes, I had the same question about how to prevent it.
>> >> > > >>>> For platform notification, if the hardware doesn't support interlocked
>> >> > > >>>> operations. I think we can use a workaround that, platform triggers
>> >> > > >>>> interrupt to OSPM without touching status field. The OSPM PCC client
>> >> > > >>>> will decide what to do with this interrupt. For example, OSPM sends a
>> >> > > >>>> consumer command to check it.
>> >> > > >>> How do we decide which platform can support this interlocked operation?
>> >> > > >>> and how do we decide between a completion notification and platform
>> >> > > >>> notification?
>> >> > > >> Truly, we should follow the specification. But I don't know if there's
>> >> > > >> any hardware support this interlocked operation.
>> >> > > >> For the decide between a completion notification and platform notification
>> >> > > >>  - Completion notification: Bit "Command Complete" is set.
>> >> > > >>  - Platform notification: Bit "Command Complete" is not set.
>> >> > > >>
>> >> > > >>> I think the ACPI spec on platform notification is quite ambiguous and it is
>> >> > > >>> best to get the necessary clarification and/or correction before implementing
>> >> > > >>> anything related to platform notification.
>> >> > > >> Agreed, a clarification inside ACPI Specification is needed
>> >> > > > This patch look good to me, as it doesn't deal with platform notification.
>> >> > > > We can try to get some clarification from spec side before handling the platform
>> >> > > > notification pieces.
>> >> > > >
>> >> > > > Reviewed-by: Prashanth Prakash <pprakash@xxxxxxxxxxxxxx>
>> >> > >
>> >> > > Do you have plan to apply this patch ?
>> >> >
>> >> > Yes.
>> >> >
>> >> > Thanks,
>> >> > Rafael
>> >> >
>> >>
>> >> Hi Rafael,
>> >>
>> >> This patch had an ACK from Prashanth.  Can you consider to merge
>> >> this patch please?
>> >
>> > Can you please resend it with the ACK?
>>
>> Correcting, it got a "Reviewed-by: Prashanth Prakash
>> <pprakash@xxxxxxxxxxxxxx>". Is it OK?
>
> Yes, it is.

Already resend.

Thanks
Hoan

>
> Thanks,
> Rafael
>