linux-kernel - Re: [PATCH v8 2/3] CMDQ: Mediatek CMDQ driver

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Message-ID: <1465205633.25607.33.camel@mtksdaap41>
Date:	Mon, 6 Jun 2016 17:33:53 +0800
From:	Horng-Shyang Liao <hs.liao@...iatek.com>
To:	Jassi Brar <jassisinghbrar@...il.com>
CC:	Matthias Brugger <matthias.bgg@...il.com>,
	Rob Herring <robh+dt@...nel.org>,
	Daniel Kurtz <djkurtz@...omium.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Devicetree List <devicetree@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-mediatek@...ts.infradead.org>,
	<srv_heupstream@...iatek.com>,
	Sascha Hauer <kernel@...gutronix.de>,
	"Philipp Zabel" <p.zabel@...gutronix.de>,
	Nicolas Boichat <drinkcat@...omium.org>,
	"CK HU" <ck.hu@...iatek.com>, cawa cheng <cawa.cheng@...iatek.com>,
	Bibby Hsieh <bibby.hsieh@...iatek.com>,
	YT Shen <yt.shen@...iatek.com>,
	Daoyuan Huang <daoyuan.huang@...iatek.com>,
	Damon Chu <damon.chu@...iatek.com>,
	"Josh-YC Liu" <josh-yc.liu@...iatek.com>,
	Glory Hung <glory.hung@...iatek.com>,
	Jiaguang Zhang <jiaguang.zhang@...iatek.com>,
	Dennis-YC Hsieh <dennis-yc.hsieh@...iatek.com>,
	Monica Wang <monica.wang@...iatek.com>,
	Jaswinder Singh <jaswinder.singh@...aro.org>
Subject: Re: [PATCH v8 2/3] CMDQ: Mediatek CMDQ driver

Hi Matthias, Jassi,

On Fri, 2016-06-03 at 18:41 +0530, Jassi Brar wrote:
> On Fri, Jun 3, 2016 at 4:48 PM, Matthias Brugger <matthias.bgg@...il.com> wrote:
> > On 03/06/16 08:12, Horng-Shyang Liao wrote:
> >> On Thu, 2016-06-02 at 10:46 +0200, Matthias Brugger wrote:
> 
> >>> I keep thinking about how to get rid of the two data structures,
> >>> task_busy_list and the task_release_wq. We need the latter for the only
> >>> sake of getting a timeout.
> >>>
> >>> Did you have a look on how the mailbox framework handles this?
> >>> By the way, what is the reason to not implement the whole driver as a
> >>> mailbox controller? For me, this driver looks like a good fit.
> >>
> >>
> >> CMDQ needs to encode commands for GCE hardware. We think this behavior
> >> should be put in CMDQ driver, and client just call CMDQ functions.
> >> Therefore, if we want to use mailbox framework, cmdq_rec must be
> >> mailbox client, and the others must be mailbox controller.
> >>
> >
> > You mean the functions to fill the cmdq_rec and execute it?
> > I think this should be part of the driver.
> >
> > Jassi, can you have a look on the interface this driver exports [0].
> > They are needed to actually create the message which will be send.
> > Could something like this be part of a mailbox driver?
> >
> > [0] https://patchwork.kernel.org/patch/9140221/
> >
> Packet creating/parsing should not be a part of controller driver. As
> the log of this patch says, today it is used for only display but in
> future it could work with other h/w as well, so it makes sense to have
> mailbox api do the message queuing, the controller driver do the
> send/receive and client drivers implement display and other h/w
> specific packaging of data (protocol handling).
> 
> So yes, I think this could use mailbox api.
> 
> Cheers.


Let me use display as an example to do some further explanation
about CMDQ in advance. You can think CMDQ is a shadow register
replacement. Therefore, we use cmdq_rec_write(_mask), cmdq_rec_wfe, and
cmdq_rec_clear_event instead of accessing registers, and use
cmdq_rec_flush(_async) instead of atomic swap.

If we use mailbox to do the message queue, we can use mailbox framework
to implement flush and callback. However, I don't think mailbox is
suitable for cmdq_rec_write(_mask), cmdq_rec_wfe, and
cmdq_rec_clear_event since they are just record some commands. Is this
the same as your comment "Packet creating/parsing should not be a part
of controller driver."?

Therefore, do you mean we use mailbox framework to implement flush and
callback and keep other interfaces? Just want to confirm that I get the
correct idea from you. Many thanks for your kindly reply.

Thanks,
HS