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

[Michal Wilczynski]

On 6/18/25 00:14, Drew Fustini wrote:
> 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?

Yeah it doesn't matter, I asked simply because it would be better in the
DT to accurately describe the HW. I would omit the 'clock-frequency'
altogether, but doing that makes the driver probe fail.

> 
> Thanks,
> Drew
> 
> [1] https://protect2.fireeye.com/v1/url?k=260051e8-477bfb60-2601daa7-74fe4860018a-782a548f971ff58f&q=1&e=7e973bd1-ed36-4a12-af1c-1cf44bea2e5c&u=https%3A%2F%2Fgit.beagleboard.org%2Fbeaglev-ahead%2Fbeaglev-ahead%2F-%2Ftree%2Fmain%2Fdocs
> 

Best regards,
-- 
Michal Wilczynski <m.wilczynski@xxxxxxxxxxx>