linux-kernel - Re: [PATCH v2 2/4] dt-bindings: mailbox: mediatek: gce-mailbox: Add reference to gce-props.yaml

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Date: Tue, 16 Jan 2024 17:22:57 +0000
From: Conor Dooley <conor@...nel.org>
To: Jason-JH Lin (林睿祥) <Jason-JH.Lin@...iatek.com>
Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mediatek@...ts.infradead.org" <linux-mediatek@...ts.infradead.org>,
	"robh+dt@...nel.org" <robh+dt@...nel.org>,
	Johnson Wang (王聖鑫) <Johnson.Wang@...iatek.com>,
	Singo Chang (張興國) <Singo.Chang@...iatek.com>,
	"linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
	"chunkuang.hu@...nel.org" <chunkuang.hu@...nel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Jason-ch Chen (陳建豪) <Jason-ch.Chen@...iatek.com>,
	Shawn Sung (宋孝謙) <Shawn.Sung@...iatek.com>,
	Nancy Lin (林欣螢) <Nancy.Lin@...iatek.com>,
	"conor+dt@...nel.org" <conor+dt@...nel.org>,
	Project_Global_Chrome_Upstream_Group <Project_Global_Chrome_Upstream_Group@...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>,
	"jassisinghbrar@...il.com" <jassisinghbrar@...il.com>,
	"angelogioacchino.delregno@...labora.com" <angelogioacchino.delregno@...labora.com>
Subject: Re: [PATCH v2 2/4] dt-bindings: mailbox: mediatek: gce-mailbox: Add
 reference to gce-props.yaml

On Tue, Jan 16, 2024 at 08:21:15AM +0000, Jason-JH Lin (林睿祥) wrote:
> On Mon, 2024-01-15 at 17:23 +0000, Conor Dooley wrote:
> > On Fri, Jan 12, 2024 at 07:44:13AM +0000, Jason-JH Lin (林睿祥) wrote:
> > > On Thu, 2024-01-11 at 17:31 +0000, Conor Dooley wrote:
> > > > On Wed, Jan 10, 2024 at 04:36:20PM +0000, Jason-JH Lin (林睿祥)

> > > > > 2. We'll have the secure CMDQ mailbox driver in the future
> > > > > patch
> > > > > [1].
> > > > > It will request or reserve a mailbox channel, which is a
> > > > > dedicate
> > > > > GCE
> > > > > thread, as a secure IRQ handler. This GCE thread executes a
> > > > > looping
> > > > > instruction set that keeps waiting for the gce-event set from
> > > > > another
> > > > > GCE thread in the secure world. So we also need to tell the
> > > > > CMDQ
> > > > > driver
> > > > > what gce-event need to be waited.
> > > > 
> > > > Ditto here, what level does this vary at? Do different SoCs or
> > > > different
> > > > boards/platforms dictate the value?
> > > 
> > > It's a SoC level, the SoC supports secure feature will need this
> > > property.
> > > 
> > > > Could this channel be determined from the soc-specific
> > > > compatible?
> > > > 
> > > > In other words, please explain in your commit message why this
> > > > requires
> > > > a property and is not detectable from any existing mechanism.
> > > > From
> > > > reading this I don't know what is preventing the secure mailbox
> > > > channel
> > > > from picking a "random" unused channel.
> > > 
> > > The secure channel could be dedicated from the soc-specific
> > > compatible,
> > > but the event ID couldn't.
> > > 
> > > The same event signal corresponding event ID may changes in
> > > different
> > > SoC.
> > > E.g.
> > > The HW event signal for CMDQ_EVENT_VDO0_MUTEX_STREAM_DONE_0 is
> > > corresponding to GCE event ID: 574 in MT8188, but it's
> > > corresponding to
> > > eventID: 597 in MT8195.
> > 
> > Is it always 574 in MT8188 and always 597 in MT8195?
> > 
> Yes, some gce-events are hardware bound and they can not change by
> software. For example, in MT8195, when VDO0_MUTEX is stream done,
> VDO_MUTEX will send an event signal to GCE, and the value of event
> ID:597 will be set to 1. In MT8188, the value of event ID: 574 will be
> set to 1 when VOD0_MUTEX is stream done.
> 
> Some of gce-events are not hardware bound and they can change by
> software. For example, in MT8188, we can take the event ID: 855 that is
> not bound to any hardware to set its value to 1 when the driver in
> secure world completes a task. But in MT8195, the event ID: 855 is
> already bound to VDEC_LAT1, so we have to take another event ID to
> achieve the same purpose.
> This event ID can be change any IDs that is not bound to any hardware
> and is not use in any software driver yet.
> We can see if the event ID is bound to the hardware or is used by
> software driver in the header
> include/de-bindings/mailbox/mediatek,mt8188-gce.h.

I see. Bring this particular patch back with your future series that
adds support for the secure channel then.

Thanks,
Conor.

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