Re: [PATCH 2/2] clk: qcom: gcc-sc8280xp: Don't keep display AHB clocks always-on

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On 10/2/23 10:34, Johan Hovold wrote:
On Sat, Sep 30, 2023 at 06:44:47PM +0200, Konrad Dybcio wrote:
On 9/30/23 11:39, Johan Hovold wrote:
On Fri, Sep 29, 2023 at 03:38:53PM +0200, Konrad Dybcio wrote:
These clocks are consumed by the dispcc[01] clock controllers, so there's
no reason to keep them on from gcc probe. Remove that hack.

Eh, how did you test this patch?

Oehh you're right, I didn't notice that I still had clk_ignore_unused :/

That doesn't matter since these clocks are never even registered with
the clock framework.
That's the point, if it was missing and was not enabled I would have noticed display not working (unless the bootloader left it on, which it did for at least the mdss instance with the eDP panel)


But you'd notice that if you try to verify the clock state by looking at
/sys/kernel/debug/clk/clk_summary for example.

The GCC_DISP_AHB_CLK clocks are not modelled by the clock driver
currently so nothing is guaranteeing them to be enabled if we were to
apply this patch. They just happen to be left on by the bootloader on
some machines currently (well at least one of them is on one machine).

What fooled me is that despite not being modeled by the clock driver, it
is defined in bindings and referenced in the device tree.

Another thing I'll fix up!

Right, a number of Qualcomm SoCs apparently fail to register these
clocks. You should start by determining why that is as I assume (hope)
it was done for a reason.
The reason is, downstream lazily enables clocks because people decided they don't leak much power and are still enabled after a clock controller reset (or something) and we started blindly copying that around 2017 :/


Then the Qualcomm drivers use sloppy bulk clock look-up and enable so
that an integrator would never even notice when clocks are missing. Once
the clocks are registered, that could be tightened up as well.
Yeah the current state of things is not great.

Konrad




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