Re: [PATCH v2 4/9] drm/panthor: Implement optional reset

[Boris Brezillon <boris.brezillon@collabora.com>]

On Thu, 4 Sep 2025 15:49:31 +0200
Marek Vasut <marek.vasut@mailbox.org> wrote:

> >> I suspect the extra soft reset I did before "un-halted" the GPU and
> >> allowed it to proceed.  
> > 
> > Hm, not quite. I mean, you still need to explicitly boot the MCU after
> > a reset, which is what the write to MCU_CONTROL [1] does. What the
> > soft-reset does though, is reset all GPU blocks, including the MCU.
> > This means the MCU starts from a fresh state when you reach [1].  
> 
> I have a feeling the write to MCU_CONTROL does nothing in my case.

I believe it does, otherwise you wouldn't be able to kick the MCU
and get things working until the first runtime suspend happens. I gut
feeling is that there's something fishy in the FW or SoC integration
that causes the FW HALT request to put the MCU/GPU in a bad state
preventing further MCU_CONTROL(AUTO_START) from functioning correctly
after that point.

> 
> Is there some way to probe the MCU state before/after setting GLB_HALT, 
> and also before/after the MCU_CONTROL write, using 
> gpu_read()/gpu_write() register operations, to find out what is going on 
> with the MCU at each point ?

Yes, there's an MCU_STATUS register [1].

[1]https://elixir.bootlin.com/linux/v6.16.4/source/drivers/gpu/drm/panthor/panthor_fw.c#L1045