i.MX8M GPU max clock

[gary_bisson]

Hi,

Both the TRM and Datasheet mention the GC7000L GPU as being able to run @1GHz (shader clock).

• See "i.MX 8M Dual/8M QuadLite/8M Quad Applications Processors Reference Manual, Rev. 0, 01/2018" Table 5-1 Clock Root Table
• Or "i.MX 8M Dual / 8M QuadLite / 8M Quad Applications Processors Data Sheet for Consumer Products, Rev. 0, 01/2018" Table 7 Operating ranges

However in every branch that support i.MX8MQ processors, that shader clock is clearly limited to 800MHz:

https://source.codeaurora.org/external/imx/linux-imx/tree/arch/arm64/boot/dts/freescale/fsl-imx8mq.d... 

fsl-imx8mq.dtsi\freescale\dts\boot\arm64\arch - linux-imx - i.MX Linux kernel 

Can you explain that limitation? Have you had issues running the shader clock @1GHz?

Regards,

Gary

[gary_bisson]

Hi,

Any update on this?

Regards,

Gary

[gusarambula]

Hello Gary,

My apologies. I checked with our experts and I’m still looking for more details on this. The data on the documents you mentioned is correct, gc7000lite gpu core has 800MHz max clock, gc7000 in imx8qm may reach 1GHz. It could be that the actual shader clock is generated from the root clock and is not the root clock itself (although I personally find it unlikely) or it could be that the code was ported from the gc7000lite and thus limits the clock to 800Mhz.

I’ll let you know as soon as I find more information.

Regards,

Gustavo

[gary_bisson]

Hi Gustavo,

I think you misread my first post:

- I'm only talking about i.MX8MQ (GC7000lite), not i.MX8QM (GC7000)

- The i.MX8MQ docs do say GC7000Lite can go up to 1GHz (see first post for doc references)

Do you have other documents that say otherwise? If so, please provide a link to them.

All the documents I point to in my first post come from your website:

i.MX 8M Applications Processor | Arm® Cortex®-A53, Cortex-M4 | 4K display resolution |NXP 

Regards,

Gary

[gary_bisson]

Hi,

Forgot to mention that Vivante also says GC7000Lite can support 1GHz speed:

Vivante GC7000 GPUs Deliver Desktop-Class Graphics to Mobile Devices 

Regards,

Gary

[gusarambula]

Hello Gary,

You are right. My mistake. The information that the gc7000lite gpu core has 800MHz max clock came from our experts. Let me double check with them to see what information is correct. The i.MX8M Datasheet (Rev. 0.1, 05/2018) does specify a nominal and an overdrive mode:

Nominal mode—the maximum GPU frequency supported in this mode is 800 MHz.

Overdrive mode—the maximum GPU frequency supported in this mode is 1 GHz.

So perhaps the BSP uses the nominal mode while the overdrive is also valid. Let me also check why would only 800Mhz be implemented.

I'll keep you informed.

Regards,

Gustavo

[gusarambula]

Hello Gary,

I confirmed that in the BSP release 800MHz@0.9V (Nominal mode) is the recommended mode. The data sheet says GPU can work at 1GHz@1.0V (Overdrive mode) and this is correct, it can work at 1GHz, but this is not the recommended mode.

Regards,

[cphealy1]

Hi Gustavo,

I have an i.MX8M use case where the GPU pixel rate needs to be as high as possible.  If we want to run the GPU at 1Ghz instead of 800Mhz, given what you are saying about overheating, can we simply reduce the CPU frequency by some amount to offset the increased GPU thermal load and successfully run the 3D GPU at 1Ghz?

Is there any additional data regarding running the GPU at a higher frequency from a thermal standpoint?

Regards,

Chris

[cphealy1]

To reply to my own question, we changed the GC7000lite GPU frequency to 1GHz and gained ~20% graphics framerate.  Even with the GPU frequency increased to 1GHz, we don't have any thermal problems.  This is likely due to our thermal design which has the i.MX8M connected to a large heat sink.

[gary_bisson]

Hi,

Thanks for confirming the doc is correct! However, can you explain why it isn't the recommended mode? Is there any overheating issue when running @1GHz?

Why do you set the CPU to be in overdrive mode by default (1.5GHz @1V instead of nominal 1GHz @0.9V) but not the GPU? Same goes for the VPU, it is in overdrive mode by default.

Regards,

Gary

[gusarambula · Accepted solution]

Hello Gary,

Yes, the main reason why the recommended mode for the GPU is nominal and not overdrive is due to overheating. You could use the overdrive mode but you would need to make sure that the extra heat generated can be dissipated.

The different modules contribute to the generated heat differently so that’s why other modules are set to overdrive by default. The BSP is configured with the NXP boards in mind and their specific heatsink configuration but your design may differ.

I hope this answers your question!

Regards,

Gustavo

[gary_bisson]

Hi Gustavo,

Yes that answers my question.

Thanks,

Gary