Re: [PATCH v2 10/11] drm/mediatek: Add cmdq_insert_backup_cookie before secure pkt finalize

From: "CK Hu (胡俊光)" <ck.hu@mediatek.com>
To: "matthias.bgg@gmail.com" <matthias.bgg@gmail.com>,
	"Jason-JH Lin (林睿祥)" <Jason-JH.Lin@mediatek.com>,
	"angelogioacchino.delregno@collabora.com"
	<angelogioacchino.delregno@collabora.com>,
	"robh+dt@kernel.org" <robh+dt@kernel.org>,
	"krzysztof.kozlowski+dt@linaro.org"
	<krzysztof.kozlowski+dt@linaro.org>,
	"chunkuang.hu@kernel.org" <chunkuang.hu@kernel.org>
Cc: "jkardatzke@google.com" <jkardatzke@google.com>,
	"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
	"conor+dt@kernel.org" <conor+dt@kernel.org>,
	Project_Global_Chrome_Upstream_Group
	<Project_Global_Chrome_Upstream_Group@mediatek.com>,
	"Singo Chang (張興國)" <Singo.Chang@mediatek.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"dri-devel@lists.freedesktop.org"
	<dri-devel@lists.freedesktop.org>,
	"linaro-mm-sig@lists.linaro.org" <linaro-mm-sig@lists.linaro.org>,
	"Jason-ch Chen (陳建豪)" <Jason-ch.Chen@mediatek.com>,
	"Nancy Lin (林欣螢)" <Nancy.Lin@mediatek.com>,
	"Johnson Wang (王聖鑫)" <Johnson.Wang@mediatek.com>,
	"Shawn Sung (宋孝謙)" <Shawn.Sung@mediatek.com>,
	"linux-mediatek@lists.infradead.org"
	<linux-mediatek@lists.infradead.org>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>,
	"linux-media@vger.kernel.org" <linux-media@vger.kernel.org>
Subject: Re: [PATCH v2 10/11] drm/mediatek: Add cmdq_insert_backup_cookie before secure pkt finalize
Date: Mon, 6 Nov 2023 01:36:06 +0000	[thread overview]
Message-ID: <cde7fe7dd8e7b26954c1cdfb132d9aa1b6f51745.camel@mediatek.com> (raw)
In-Reply-To: <393154d13115196fde483cc840393719a8844fc1.camel@mediatek.com>

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On Sun, 2023-11-05 at 13:35 +0000, Jason-JH Lin (林睿祥) wrote:
> Hi CK,
> 
> On Thu, 2023-10-26 at 02:26 +0000, CK Hu (胡俊光) wrote:
> > Hi, Jason:
> > 
> > On Mon, 2023-10-23 at 12:45 +0800, Jason-JH.Lin wrote:
> > > Add cmdq_insert_backup_cookie to append some commands before EOC:
> > > 1. Get GCE HW thread execute count from the GCE HW register.
> > > 2. Add 1 to the execute count and then store into a shared
> > > memory.
> > 
> > I think when cmdq driver handler interrupt, it could simply call
> > into
> > TEE with an API to query status. The status not only the execute
> > count,
> > but also other message including error information. So it's not
> > necessary to use such non-tricky way to get execute count.
> 
> The reason why we use shared memory to record execute count here is:
> 1. normal world can not access the register of secure GCE thread in
> normal world.
> 2. calling TEE invoke cmd in the irq handler would be expensive and
> not
> stable. I've tested that a single TEE invloke cmd to CMDQ PTA costs
> 19~53 us. Maybe it would cost more during the scenario that needs
> more
> CPU loading.

Add this to comment.

> 
> > 
> > One more question. The command buffer is not secure. Does the GCE
> > hardware execute this non-secure command buffer?
> > 
> 
> GCE command buffer is generate in the normal world first. Then it
> will
> be copied to the shared memory and pass to the secure world. All the
> instruction in command buffer will be verified in secure world then
> they will be copied to the secure command buffer and executed by GCE
> secure thread. I'll add this information to the cover letter at the
> next version.
> 
> Regards
> Jason-JH.Lin
> 
> > Regards,
> > CK
> > 