Re: [PATCH v2 0/7] Add dts for mt8183 GPU (and misc panfrost patches)

[Steven Price <steven.price@arm.com>]

On 08/01/2020 05:23, Nicolas Boichat wrote:
> Hi!
> 
> Sorry for the long delay since https://patchwork.kernel.org/patch/11132381/,
> finally got around to give this a real try.
> 
> The main purpose of this series is to upstream the dts change and the binding
> document, but I wanted to see how far I could probe the GPU, to check that the
> binding is indeed correct. The rest of the patches are RFC/work-in-progress, but
> I think some of them could already be picked up.
> 
> So this is tested on MT8183 with a chromeos-4.19 kernel, and a ton of
> backports to get the latest panfrost driver (I should probably try on
> linux-next at some point but this was the path of least resistance).
> 
> I tested it as a module as it's more challenging (originally probing would
> work built-in, on boot, but not as a module, as I didn't have the power
> domain changes, and all power domains are on by default during boot).
> 
> Probing logs looks like this, currently:
> [  221.867726] panfrost 13040000.gpu: clock rate = 511999970
> [  221.867929] panfrost 13040000.gpu: Linked as a consumer to regulator.14
> [  221.868600] panfrost 13040000.gpu: Linked as a consumer to regulator.31
> [  221.870586] panfrost 13040000.gpu: Linked as a consumer to genpd:0:13040000.gpu
> [  221.871492] panfrost 13040000.gpu: Linked as a consumer to genpd:1:13040000.gpu
> [  221.871866] panfrost 13040000.gpu: Linked as a consumer to genpd:2:13040000.gpu
> [  221.872427] panfrost 13040000.gpu: mali-g72 id 0x6221 major 0x0 minor 0x3 status 0x0
> [  221.872439] panfrost 13040000.gpu: features: 00000000,13de77ff, issues: 00000000,00000400
> [  221.872445] panfrost 13040000.gpu: Features: L2:0x07120206 Shader:0x00000000 Tiler:0x00000809 Mem:0x1 MMU:0x00002830 AS:0xff JS:0x7
> [  221.872449] panfrost 13040000.gpu: shader_present=0x7 l2_present=0x1
> [  221.873526] panfrost 13040000.gpu: error powering up gpu stack
> [  221.878088] [drm] Initialized panfrost 1.1.0 20180908 for 13040000.gpu on minor 2
> [  221.940817] panfrost 13040000.gpu: error powering up gpu stack
> [  222.018233] panfrost 13040000.gpu: error powering up gpu stack
> (repeated)

It's interesting that it's only the stack that is failing. In hardware there's a dependency: L2->stack->shader - so in theory the shader cores shouldn't be able to power up either. There are some known hardware bugs here though[1]:

	MODULE_PARM_DESC(corestack_driver_control,
			"Let the driver power on/off the GPU core stack independently "
			"without involving the Power Domain Controller. This should "
			"only be enabled on platforms for which integration of the PDC "
			"to the Mali GPU is known to be problematic.");

[1] https://github.com/ianmacd/d2s/blob/master/drivers/gpu/arm/b_r16p0/backend/gpu/mali_kbase_pm_driver.c#L57

It might be worth just dropping the code for powering up/down stacks and let the GPU's own dependency management handle it.

Steve

> 
> So the GPU is probed, but there's an issue when powering up the STACK, not
> quite sure why, I'll try to have a deeper look, at some point.
> 
> Thanks!
> 
> Nicolas
> 
> v2:
>   - Use sram instead of mali_sram as SRAM supply name.
>   - Rename mali@ to gpu@.
>   - Add dt-bindings changes
>   - Stacking patches after the device tree change that allow basic
>     probing (still incomplete and broken).
> 
> Nicolas Boichat (7):
>    dt-bindings: gpu: mali-bifrost: Add Mediatek MT8183
>    arm64: dts: mt8183: Add node for the Mali GPU
>    drm/panfrost: Improve error reporting in panfrost_gpu_power_on
>    drm/panfrost: Add support for a second regulator for the GPU
>    drm/panfrost: Add support for multiple power domain support
>    RFC: drm/panfrost: Add bifrost compatible string
>    RFC: drm/panfrost: devfreq: Add support for 2 regulators
> 
>   .../bindings/gpu/arm,mali-bifrost.yaml        |  20 ++++
>   arch/arm64/boot/dts/mediatek/mt8183-evb.dts   |   7 ++
>   arch/arm64/boot/dts/mediatek/mt8183.dtsi      | 104 +++++++++++++++++
>   drivers/gpu/drm/panfrost/panfrost_devfreq.c   |  18 +++
>   drivers/gpu/drm/panfrost/panfrost_device.c    | 108 ++++++++++++++++--
>   drivers/gpu/drm/panfrost/panfrost_device.h    |   7 ++
>   drivers/gpu/drm/panfrost/panfrost_drv.c       |   1 +
>   drivers/gpu/drm/panfrost/panfrost_gpu.c       |  15 ++-
>   8 files changed, 267 insertions(+), 13 deletions(-)
>