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

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Date:	Mon, 15 Aug 2016 16:41:22 -0700
From:	Hoan Tran <hotran@....com>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	Jassi Brar <jassisinghbrar@...il.com>,
	Ashwin Chaugule <ashwin.chaugule@...aro.org>,
	Robert Moore <robert.moore@...el.com>,
	Alexey Klimov <alexey.klimov@....com>,
	lkml <linux-kernel@...r.kernel.org>,
	linux acpi <linux-acpi@...r.kernel.org>, Loc Ho <lho@....com>,
	Duc Dang <dhdang@....com>,
	"Prakash, Prashanth" <pprakash@...eaurora.org>
Subject: Re: [PATCH v3] mailbox: pcc: Support HW-Reduced Communication
 Subspace type 2

Hi Rafael,

On Mon, Aug 15, 2016 at 4:18 PM, Rafael J. Wysocki <rjw@...ysocki.net> 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@...ysocki.net> 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@...eaurora.org> 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@...eaurora.org> 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@....com> wrote:
>> > > >>>>> Hi Prashanth,
>> > > >>>>>
>> > > >>>>>
>> > > >>>>> On Wed, Jun 8, 2016 at 5:32 PM, Prakash, Prashanth
>> > > >>>>> <pprakash@...eaurora.org> 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@...aro.org> wrote:
>> > > >>>>>>>> + Prashanth (Can you please have a look as well?)
>> > > >>>>>>>>
>> > > >>>>>>>> On 31 May 2016 at 15:35, Hoan Tran <hotran@....com> 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@...eaurora.org>
>> > >
>> > > 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@...eaurora.org>". Is it OK?

Thanks
Hoan

>
> Thanks,
> Rafael
>