Re: [PATCH v4 2/5] clk: qcom: regmap: add pipe clk implementation

From: Johan Hovold <johan@kernel.org>
To: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Cc: "Dmitry Baryshkov" <dmitry.baryshkov@linaro.org>,
	"Andy Gross" <agross@kernel.org>,
	"Bjorn Andersson" <bjorn.andersson@linaro.org>,
	"Stephen Boyd" <swboyd@chromium.org>,
	"Michael Turquette" <mturquette@baylibre.com>,
	"Taniya Das" <quic_tdas@quicinc.com>,
	"Lorenzo Pieralisi" <lorenzo.pieralisi@arm.com>,
	"Krzysztof Wilczyński" <kw@linux.com>,
	"Bjorn Helgaas" <bhelgaas@google.com>,
	"Prasad Malisetty" <quic_pmaliset@quicinc.com>,
	"Johan Hovold" <johan+linaro@kernel.org>,
	linux-arm-msm@vger.kernel.org, linux-clk@vger.kernel.org,
	linux-pci@vger.kernel.org
Subject: Re: [PATCH v4 2/5] clk: qcom: regmap: add pipe clk implementation
Date: Fri, 6 May 2022 14:54:46 +0200	[thread overview]
Message-ID: <YnUals1FAssF2zxO@hovoldconsulting.com> (raw)
In-Reply-To: <20220502150611.GF98313@thinkpad>

On Mon, May 02, 2022 at 08:36:11PM +0530, Manivannan Sadhasivam wrote:

> If I get the logic behind this "parking" thing right, then it is required
> for producing a stable pipe_clk from GCC when the PHY is about to initialize.
> Also to make sure that there is no glitch observed on pipe_clk while
> initializing the PHY. And once it is powered ON properly, the pipe_clksrc
> should be used as the parent for pipe_clk.

No, the "parking" is only needed when toggling the corresponding GDSC
which needs a ticking source for some handshake or else it hangs.

The PHY PLL could be muxed in whenever the GDSC power domain is enabled.

That's the thing I don't like about tying the muxing to gating the pipe
clock in the PHY driver. It just happens to work as long as we remember
to gate before disabling the power domain (for a separate device, the
PCIe controller).

But that doesn't solve the case were the boot firmware has left things
in a weird state.

Johan