Re: [PATCH v4 0/8] Add TH1520 GPU support with power sequencing

[Drew Fustini <drew@pdp7.com>]

On Sat, Jun 14, 2025 at 08:06:06PM +0200, Michal Wilczynski wrote:
> This patch series introduces support for the Imagination IMG BXM-4-64
> GPU found on the T-HEAD TH1520 SoC. A key aspect of this support is
> managing the GPU's complex power-up and power-down sequence, which
> involves multiple clocks and resets.
> 
> The TH1520 GPU requires a specific sequence to be followed for its
> clocks and resets to ensure correct operation. Initial discussions and
> an earlier version of this series explored managing this via the generic
> power domain (genpd) framework. However, following further discussions
> with kernel maintainers [1], the approach has been reworked to utilize
> the dedicated power sequencing (pwrseq) framework.
> 
> This revised series now employs a new pwrseq provider driver
> (pwrseq-thead-gpu.c) specifically for the TH1520 GPU. This driver
> encapsulates the SoC specific power sequence details. The Imagination
> GPU driver (pvr_device.c) is updated to act as a consumer of this power
> sequencer, requesting the "gpu-power" target. The sequencer driver,
> during its match phase with the GPU device, acquires the necessary clock
> and reset handles from the GPU device node to perform the full sequence.
> 
> This approach aligns with the goal of abstracting SoC specific power
> management details away from generic device drivers and leverages the
> pwrseq framework as recommended.
> 
> The series is structured as follows:
> 
> Patch 1: Introduces the pwrseq-thead-gpu auxiliary driver to manage the
>          GPU's power-on/off sequence.
> Patch 2: Adds device tree bindings for the gpu-clkgen reset to the
>          existing thead,th1520-aon binding.
> Patch 3: Extends the pm-domains driver to detect the gpu-clkgen reset
>          and spawn the pwrseq-thead-gpu auxiliary driver.
> Patch 4: Updates the Imagination DRM driver to utilize the pwrseq
>          framework for TH1520 GPU power management.
> Patch 5: Adds the thead,th1520-gpu compatible string to the PowerVR GPU
>          device tree bindings.
> Patch 6: Adds the gpu-clkgen reset property to the aon node in the
>          TH1520 device tree source.
> Patch 7: Adds the device tree node for the IMG BXM-4-64 GPU and its
>          required fixed-clock.
> Patch 8: Enables compilation of the Imagination PowerVR driver on the
>          RISC-V architecture.
> 
> This patchset finishes the work started in bigger series [2] by adding
> all remaining GPU power sequencing piece. After this patchset the GPU
> probes correctly.
> 
> This series supersedes the previous genpd based approach. Testing on
> T-HEAD TH1520 SoC indicates the new pwrseq based solution works
> correctly.
> 
> An open point in Patch 7/8 concerns the GPU memory clock (gpu_mem_clk),
> defined as a fixed-clock. The specific hardware frequency for this clock
> on the TH1520 could not be determined from available public
> documentation. Consequently, clock-frequency = <0>; has been used as a
> placeholder to enable driver functionality.
> 

I don't have any more information that what is in the public PDFs [1],
so I think it is okay to have a placeholder frequency.

Is it the case that the frequency doesn't really matter from the
perspective of the driver?

Thanks,
Drew

[1] https://git.beagleboard.org/beaglev-ahead/beaglev-ahead/-/tree/main/docs