Re: [PATCH v14] arm64: dts: mt8183: Add node for the Mali GPU

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On Fri, May 21, 2021 at 8:01 PM Nicolas Boichat [off-list ref] wrote:

Add a basic GPU node for mt8183, as well as OPP table.

Note that with the current panfrost driver, devfreq is not
actually functional, as the we do not have platform-specific
support for >1 supplies. Also, we are missing code to handle
frequency change, as the GPU frequency needs to be switched
away to a stable 26Mhz clock during the transition.

Signed-off-by: Nicolas Boichat <redacted>
---
The binding we use with out-of-tree Mali drivers includes more
clocks, this is used for devfreq: the out-of-tree driver switches
clk_mux to clk_sub_parent (26Mhz), adjusts clk_main_parent, then
switches clk_mux back to clk_main_parent:
(see https://chromium.googlesource.com/chromiumos/third_party/kernel/+/chromeos-4.19/drivers/gpu/arm/midgard/platform/mediatek/mali_kbase_runtime_pm.c#423)
clocks =
        <&topckgen CLK_TOP_MFGPLL_CK>,
        <&topckgen CLK_TOP_MUX_MFG>,
        <&clk26m>,
        <&mfgcfg CLK_MFG_BG3D>;
clock-names =
        "clk_main_parent",
        "clk_mux",
        "clk_sub_parent",
        "subsys_mfg_cg";
(based on discussions, this probably belongs in the clock core)

This only matters for devfreq, that is disabled anyway as we don't
have platform-specific code to handle >1 supplies.

Yes. This can be done with clk_notifiers. See

    https://elixir.bootlin.com/linux/latest/source/drivers/clk/sunxi-ng/ccu_mux.c#L261

for such an example.


ChenYu