linux-kernel - Re: [PATCH] clk: qcom: gcc-msm8953: fix stuck gcc_usb30_master

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Message-ID: <07937184481af74c65108bae26526605.sboyd@kernel.org>
Date:   Mon, 23 Oct 2023 19:59:02 -0700
From:   Stephen Boyd <sboyd@...nel.org>
To:     Andy Gross <agross@...nel.org>,
        Barnabás Czémán <trabarni@...il.com>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Michael Turquette <mturquette@...libre.com>,
        linux-arm-msm@...r.kernel.org, linux-clk@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] clk: qcom: gcc-msm8953: fix stuck gcc_usb30_master_clk

Quoting Konrad Dybcio (2023-10-06 16:50:18)
> On 2.10.2023 19:00, Barnabás Czémán wrote:
> > According to downstream dwc3-msm source this clock has FSM dependency on
> > gcc_pcnoc_usb30_clk so enabling it would fail if latter isn't enabled.
> > This patch add works around this issue by changing parent of
> > gcc_usb30_master_clk to gcc_pcnoc_usb30_clk. This is acceptable because
> > both clocks have same parent and are branches/gates.
> > 
> > Signed-off-by: Barnabás Czémán <trabarni@...il.com>
> > ---
> "meh"
> 
> There are multiple cases, especially with qcom, where there are some
> magic "dependencies" without parent-child relationship. The common
> clock framework doesn't currently have any good way to handle this,
> other than some mind gymnastics like you had to do here with matching
> them against a common parent/ancestor..
> 
> Stephen, what do you say?
> 

You can't change the parent to be not the actual parent. The consumer of
the branch probably wants to call clk_set_rate() on the branch and have
it propagate up to the parent to set the actual rate. Can the axi clk
simply be left enabled all the time? That seems simpler. Otherwise we
probably need to leave the axi clk control to the interconnect driver
and make sure drivers enable interconnects before enabling this branch.

When things start to get this tangled I tend to think that we need to
remove control of the clk from the general drivers and put the logic to
control interconnects and clks into some SoC glue driver and expose a
single interface, like genpd power_on/power_off so that general drivers
can't get the sequence of steps wrong. Instead all they can do is "power
on" their device, and the SoC glue driver can do the proper sequence of
framework calls to power up the device.