linux-kernel - Re: [PATCH v2 2/3] dt-bindings: power: Add mediatek larb definition

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Message-ID: <3b04c5344435cdb941b5d132e8f5fbfdf9188d67.camel@mediatek.com>
Date: Thu, 28 Mar 2024 06:06:16 +0000
From: Yu-chang Lee (李禹璋) <Yu-chang.Lee@...iatek.com>
To: "amergnat@...libre.com" <amergnat@...libre.com>,
	"krzysztof.kozlowski@...aro.org" <krzysztof.kozlowski@...aro.org>
CC: "linux-mediatek@...ts.infradead.org" <linux-mediatek@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	MandyJH Liu (劉人僖) <MandyJH.Liu@...iatek.com>,
	"conor+dt@...nel.org" <conor+dt@...nel.org>,
	Project_Global_Chrome_Upstream_Group
	<Project_Global_Chrome_Upstream_Group@...iatek.com>, "robh@...nel.org"
	<robh@...nel.org>, Xiufeng Li (李秀峰)
	<Xiufeng.Li@...iatek.com>, "linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, "krzysztof.kozlowski+dt@...aro.org"
	<krzysztof.kozlowski+dt@...aro.org>, "matthias.bgg@...il.com"
	<matthias.bgg@...il.com>, "ulf.hansson@...aro.org" <ulf.hansson@...aro.org>,
	Fan Chen (陳凡) <fan.chen@...iatek.com>,
	"angelogioacchino.delregno@...labora.com"
	<angelogioacchino.delregno@...labora.com>
Subject: Re: [PATCH v2 2/3] dt-bindings: power: Add mediatek larb definition

On Wed, 2024-03-27 at 12:55 +0100, Alexandre Mergnat wrote:
>  	 
> External email : Please do not click links or open attachments until
> you have verified the sender or the content.
>  Hello Yu-chang Lee,
> 
> SMI LARB must have a power domain, according to "mediatek,smi-
> larb.yaml"
> Now you try to create a link from power domain to larb.
> 
> Here is my understanding: when you enable/disable power domain, the
> larb linked to this power domain may have an issue. Then you want to
> retrieve de LARB linked to the power domain though the dts to manage
> the LARB. 

Yes, this is what I am trying to do.

> IMHO, using the dts to have this information into the power
> driver isn't necessary and may introduce some bugs if the LARB node
> and power node in the DTS aren't aligned.
> 
> It seems not implemented today but during the LARB probe, it should
> "subscribe" to the linked power domain. Then, when the power domain
> status is changing, it is able to "notify" (callback) the LARB, then
> implement the good stuff to handle this power domain status change
> into LARB driver.
> 

The problem with this method and why "smi clamp" is in power domain
driver is that our HW designer gave us a programming guide strictly
states the sequence of what we need to do to power on/off power domain.
Using callback, this sequence is no longer guaranteed and the side
effect is unknown... 

So I would like to stick with adding larbs just like smi into power
domain node.

> Regards,
> Alexandre

Best Regards,
Yu-chang
> 
> On Wed, Mar 27, 2024 at 12:04 PM Krzysztof Kozlowski
> <krzysztof.kozlowski@...aro.org> wrote:
> >
> > On 27/03/2024 11:56, Yu-chang Lee (李禹璋) wrote:
> > > On Wed, 2024-03-27 at 11:43 +0100, Krzysztof Kozlowski wrote:
> > >>
> > >> External email : Please do not click links or open attachments
> until
> > >> you have verified the sender or the content.
> > >>  On 27/03/2024 11:39, Yu-chang Lee (李禹璋) wrote:
> > >>>>>>
> > >>>>> Hi,
> > >>>>>
> > >>>>> I will double check the format of yaml for the next version,
> > >> sorry
> > >>>> for
> > >>>>> inconvenience. But I did test it on mt8188 chromebook, the
> reason
> > >>>> why
> > >>>>
> > >>>> How do you test a binding on chromebook?
> > >>>>
> > >>>>> power domain need larb node is that when mtcmos power on,
> signal
> > >>>> glitch
> > >>>>> may produce. Power domain driver must reset larb when this
> happen
> > >>>> to
> > >>>>> prevent dummy transaction on bus. That why I need larb node
> in
> > >> dts.
> > >>>>
> > >>>> No one talks here about larb node...
> > >>>
> > >>> Sorry, May you elaborate on what information I need to provide
> to
> > >> you
> > >>> or it is just a syntax problem I need to fix?
> > >>
> > >> Please explain the purpose of this property (how is it going to
> be
> > >> used by drivers)and what does it represent.
> > >>
> > >
> > > It represent SMI LARB(Local ARBitration). In power domain driver
> when
> > > power on power domain, It need to reset LARB to prevent potential
> power
> > > glitch which may cause dummy transaction on bus. Without taking
> care of
> > > this issue it often leads to camera hang in stress test.
> >
> > That sounds rather like missing resets... or something else
> connecting
> > these devices. Maybe the explanation is just imprecise...
> >
> > Best regards,
> > Krzysztof
> >
> >