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

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Date: Wed, 27 Mar 2024 12:55:16 +0100
From: Alexandre Mergnat <amergnat@...libre.com>
To: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>, 
	Yu-chang Lee (李禹璋) <yu-chang.lee@...iatek.com>
Cc: MandyJH Liu (劉人僖) <MandyJH.Liu@...iatek.com>, 
	"conor+dt@...nel.org" <conor+dt@...nel.org>, "robh@...nel.org" <robh@...nel.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>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, 
	"linux-mediatek@...ts.infradead.org" <linux-mediatek@...ts.infradead.org>, 
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>, 
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>, 
	Project_Global_Chrome_Upstream_Group <Project_Global_Chrome_Upstream_Group@...iatek.com>, 
	Xiufeng Li (李秀峰) <Xiufeng.Li@...iatek.com>, 
	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.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

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. 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.

Regards,
Alexandre

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
>
>