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From: Bjorn Andersson <bjorn.andersson@linaro.org>
To: Stephen Boyd <swboyd@chromium.org>
Cc: Prasad Malisetty <pmaliset@codeaurora.org>,
	agross@kernel.org, bhelgaas@google.com,
	lorenzo.pieralisi@arm.com, robh+dt@kernel.org,
	svarbanov@mm-sol.com, devicetree@vger.kernel.org,
	linux-arm-msm@vger.kernel.org, linux-usb@vger.kernel.org,
	linux-kernel@vger.kernel.org, dianders@chromium.org,
	mka@chromium.org, vbadigan@codeaurora.org,
	sallenki@codeaurora.org
Subject: Re: [PATCH v4 4/4] PCIe: qcom: Add support to control pipe clk src
Date: Fri, 16 Jul 2021 15:31:55 -0500	[thread overview]
Message-ID: <YPHsu+QLWRYpYRCz@yoga> (raw)
In-Reply-To: <CAE-0n538LKQpeY_NKQF-VM3nHVxEE0B_pN4aN=sQ8iQzK+Yyxw@mail.gmail.com>

On Fri 16 Jul 14:37 CDT 2021, Stephen Boyd wrote:

> Quoting Prasad Malisetty (2021-07-16 06:58:47)
> > This is a new requirement for sc7280 SoC.
> > To enable gdsc gcc_pcie_1_pipe_clk_src should be TCXO.
> 
> Why? Can you add that detail here? Presumably it's something like the
> GDSC needs a running clk to send a reset through the flops or something
> like that.
> 

Which presumably means that we need to "park" gcc_pcie_N_pipe_clk_src
whenever the PHY pipe is paused due to a suspend or runtime suspend.

I find this part of the commit message to primarily describing the next
patch (that is yet to be posted).

> > after PHY initialization gcc_pcie_1_pipe_clk_src needs
> > to switch from TCXO to gcc_pcie_1_pipe_clk.
> >
> > Signed-off-by: Prasad Malisetty <pmaliset@codeaurora.org>
> > ---
> >  drivers/pci/controller/dwc/pcie-qcom.c | 22 ++++++++++++++++++++++
> >  1 file changed, 22 insertions(+)
> >
> > diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
> > index 8a7a300..9e0e4ab 100644
> > --- a/drivers/pci/controller/dwc/pcie-qcom.c
> > +++ b/drivers/pci/controller/dwc/pcie-qcom.c
> > @@ -1167,6 +1170,20 @@ static int qcom_pcie_get_resources_2_7_0(struct qcom_pcie *pcie)
> >         if (ret < 0)
> >                 return ret;
> >
> > +       if (of_device_is_compatible(dev->of_node, "qcom,pcie-sc7280")) {
> > +               res->gcc_pcie_1_pipe_clk_src = devm_clk_get(dev, "pipe_mux");
> > +               if (IS_ERR(res->gcc_pcie_1_pipe_clk_src))
> > +                       return PTR_ERR(res->gcc_pcie_1_pipe_clk_src);
> > +
> > +               res->phy_pipe_clk = devm_clk_get(dev, "phy_pipe");
> > +               if (IS_ERR(res->phy_pipe_clk))
> > +                       return PTR_ERR(res->phy_pipe_clk);
> > +
> > +               res->ref_clk_src = devm_clk_get(dev, "ref");
> > +               if (IS_ERR(res->ref_clk_src))
> > +                       return PTR_ERR(res->ref_clk_src);
> > +       }
> > +
> >         res->pipe_clk = devm_clk_get(dev, "pipe");
> >         return PTR_ERR_OR_ZERO(res->pipe_clk);
> >  }
> > @@ -1255,6 +1272,11 @@ static void qcom_pcie_deinit_2_7_0(struct qcom_pcie *pcie)
> >  static int qcom_pcie_post_init_2_7_0(struct qcom_pcie *pcie)
> >  {
> >         struct qcom_pcie_resources_2_7_0 *res = &pcie->res.v2_7_0;
> > +       struct dw_pcie *pci = pcie->pci;
> > +       struct device *dev = pci->dev;
> > +
> > +       if (of_device_is_compatible(dev->of_node, "qcom,pcie-sc7280"))
> > +               clk_set_parent(res->gcc_pcie_1_pipe_clk_src, res->phy_pipe_clk);
> 
> Is anything wrong if we call clk_set_parent() here when this driver is
> running on previous SoCs where the parent is assigned via DT?

We don't assign the parent on previous platforms, we apparently just
rely on the reset value (afaict).

So I think it makes sense for all platforms to explicitly mux
pipe_clk_src to phy::pipe_clk, one the PHY is up and running.

But I was under the impression that we have the BRANCH_HALT_SKIP on the
pipe_clk because there was some sort of feedback loop to the PHY's
calibration... What this patch indicates is that we should park
pipe_clk_src onto XO at boot time, then after the PHY starts ticking we
should enable and reparent the clk_src - at which point I don't see why
we need the HALT_SKIP.

> Also, shouldn't we make sure the parent is XO at driver probe time so
> that powering on the GDSC works properly?
> 
> It all feels like a kludge though given that the GDSC is the one that
> requires the clock to be running at XO and we're working around that in
> the pcie driver instead of sticking that logic into the GDSC. What do we
> do if the GDSC is already enabled out of boot instead of being the power
> on reset (POR) configuration?
> 

What happens if we boot the device out of NVME...


PS. Are we certain that it's the PCIe driver and not the PHY that should
do this dance? I really would like to see the continuation of this patch
to see the full picture...

Regards,
Bjorn

> >
> >         return clk_prepare_enable(res->pipe_clk);
> >  }

  reply	other threads:[~2021-07-16 20:32 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-16 13:58 [PATCH v4 0/4] Add DT bindings and DT nodes for PCIe and PHY in SC7280 Prasad Malisetty
2021-07-16 13:58 ` [PATCH v4 1/4] dt-bindings: pci: qcom: Document PCIe bindings for SC720 Prasad Malisetty
2021-07-16 19:27   ` Stephen Boyd
2021-07-20  6:56     ` Prasad Malisetty
2021-07-16 13:58 ` [PATCH v4 2/4] arm64: dts: qcom: sc7280: Add PCIe and PHY related nodes Prasad Malisetty
2021-07-16 19:31   ` Stephen Boyd
2021-07-20  6:54     ` Prasad Malisetty
2021-08-02 19:23   ` Matthias Kaehlcke
2021-08-17  8:05     ` Prasad Malisetty
2021-07-16 13:58 ` [PATCH v4 3/4] arm64: dts: qcom: sc7280: Add PCIe nodes for IDP board Prasad Malisetty
2021-07-16 19:32   ` Stephen Boyd
2021-07-20  6:57     ` Prasad Malisetty
2021-07-16 13:58 ` [PATCH v4 4/4] PCIe: qcom: Add support to control pipe clk src Prasad Malisetty
2021-07-16 15:06   ` Bjorn Helgaas
2021-07-16 20:38     ` Bjorn Andersson
2021-07-20 11:28       ` Prasad Malisetty
2021-08-09 17:09       ` Prasad Malisetty
2021-07-16 19:37   ` Stephen Boyd
2021-07-16 20:31     ` Bjorn Andersson [this message]
2021-07-16 21:39       ` Stephen Boyd
2021-07-16 22:11         ` Bjorn Andersson
2021-07-16 14:29 ` [PATCH v4 0/4] Add DT bindings and DT nodes for PCIe and PHY in SC7280 Bjorn Helgaas

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