linux-kernel - Re: [PATCH v2 10/11] drm/mediatek: Add cmdq_insert_backup

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Date:   Mon, 6 Nov 2023 01:36:06 +0000
From:   CK Hu (胡俊光) <ck.hu@...iatek.com>
To:     "matthias.bgg@...il.com" <matthias.bgg@...il.com>,
        Jason-JH Lin (林睿祥) 
        <Jason-JH.Lin@...iatek.com>,
        "angelogioacchino.delregno@...labora.com" 
        <angelogioacchino.delregno@...labora.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "krzysztof.kozlowski+dt@...aro.org" 
        <krzysztof.kozlowski+dt@...aro.org>,
        "chunkuang.hu@...nel.org" <chunkuang.hu@...nel.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        Singo Chang (張興國) 
        <Singo.Chang@...iatek.com>,
        Johnson Wang (王聖鑫) 
        <Johnson.Wang@...iatek.com>,
        "linaro-mm-sig@...ts.linaro.org" <linaro-mm-sig@...ts.linaro.org>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.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>,
        "jkardatzke@...gle.com" <jkardatzke@...gle.com>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "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>
Subject: Re: [PATCH v2 10/11] drm/mediatek: Add cmdq_insert_backup_cookie
 before secure pkt finalize

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
> >