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

["Jason-JH Lin (林睿祥)" <Jason-JH.Lin@mediatek.com>]

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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.

> 
> 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
>