Re: [PATCH 2/3] PCI: dwc: qcom: Set suspend_poweroff flag for SC7280

Manivannan Sadhasivam
2022-05-18T03:52:44Z

On Tue, May 17, 2022 at 12:18:57PM -0500, Bjorn Helgaas wrote:
> [+cc Prasad, Andy, Rob, Krzysztof, Rajat, Saheed, Rama, Stephen,
> Dmitry, Kalle for connection to https://lore.kernel.org/lkml/CAE-0n53ho2DX2rqQMvvKAuDCfsWW62TceTaNPzv5Mn_NQ-U6dA@mail.gmail.com/T/]
>
> Subject line convention for this file is "PCI: qcom:" (not "PCI: dwc:
> qcom:").
>
> Find this from "git log --oneline drivers/pci/controller/dwc/pcie-qcom.c".
>
> On Tue, May 17, 2022 at 08:41:34PM +0530, Manivannan Sadhasivam wrote:
> > On Mon, May 16, 2022 at 03:19:50PM -0500, Bjorn Helgaas wrote:
> > > On Fri, May 13, 2022 at 04:30:26PM +0530, Manivannan Sadhasivam wrote:
> > > > For aggressive power saving on SC7280 SoCs, the power for the
> > > > PCI devices will be taken off during system suspend. Hence,
> > > > notify the same to the PCI device drivers using
> > > > "suspend_poweroff" flag so that the drivers can prepare the PCI
> > > > devices to handle the poweroff and recover them during resume.
> > >
> > > No doubt "power ... will be taken off during system suspend" is
> > > true, but this isn't very informative. Is this a property of
> > > SC7280? A choice made by the SC7280 driver? Why is this not
> > > applicable to other systems?
> >
> > The SC7280's RPMh firmware is cutting off the PCIe power domain
> > during system suspend. And as I explained in previous patch, the RC
> > driver itself may put the devices in D3cold conditionally on this
> > platform. The reason is to save power as this chipset is being used
> > in Chromebooks.
>
> It looks like this should be squashed into the patch you mentioned:
> https://lore.kernel.org/lkml/CAE-0n53ho2DX2rqQMvvKAuDCfsWW62TceTaNPzv5Mn_NQ-U6dA@mail.gmail.com/T/
>
> If Prasad's patch is applied without this, devices will be powered
> off, but nvme will not be prepared for it. Apparently something would
> be broken in that case?
>

Yes, but Prasad's patch is not yet reviewed so likely not get merged until
further respins.

> Also, I think this patch should be reordered so the nvme driver is
> prepared for suspend_poweroff before the qcom driver starts setting
> it. Otherwise there's a window where qcom sets suspend_poweroff and
> powers off devices, but nvme doesn't know about it, and I assume
> something will be broken in that case?
>

As per my understanding, patches in a series should not have build dependency
but they may depend on each other for functionality.

But I don't have any issue in reordering the patches. Will do.

> Please mention RPMh in the commit log, along with the specific
> connection with system suspend, i.e., what OS action enables RPMh to
> cut power.
>

Okay, will do.

Thanks,
Mani

> > > > Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
> > > > ---
> > > > drivers/pci/controller/dwc/pcie-qcom.c | 6 ++++++
> > > > 1 file changed, 6 insertions(+)
> > > >
> > > > diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
> > > > index 6ab90891801d..4b0ad2827f8f 100644
> > > > --- a/drivers/pci/controller/dwc/pcie-qcom.c
> > > > +++ b/drivers/pci/controller/dwc/pcie-qcom.c
> > > > @@ -199,6 +199,7 @@ struct qcom_pcie_cfg {
> > > > unsigned int has_ddrss_sf_tbu_clk:1;
> > > > unsigned int has_aggre0_clk:1;
> > > > unsigned int has_aggre1_clk:1;
> > > > + unsigned int suspend_poweroff:1;
> > > > };
> > > >
> > > > struct qcom_pcie {
> > > > @@ -1220,6 +1221,10 @@ static int qcom_pcie_init_2_7_0(struct qcom_pcie *pcie)
> > > > if (pcie->cfg->pipe_clk_need_muxing)
> > > > clk_set_parent(res->pipe_clk_src, res->ref_clk_src);
> > > >
> > > > + /* Indicate PCI device drivers that the power will be taken off during system suspend */
> > > > + if (pcie->cfg->suspend_poweroff)
> > > > + pci->pp.bridge->suspend_poweroff = true;
> > > > +
> > > > ret = clk_bulk_prepare_enable(res->num_clks, res->clks);
> > > > if (ret < 0)
> > > > goto err_disable_regulators;
> > > > @@ -1548,6 +1553,7 @@ static const struct qcom_pcie_cfg sc7280_cfg = {
> > > > .ops = &ops_1_9_0,
> > > > .has_tbu_clk = true,
> > > > .pipe_clk_need_muxing = true,
> > > > + .suspend_poweroff = true,
> > > > };
> > > >
> > > > static const struct dw_pcie_ops dw_pcie_ops = {
> > > > --
> > > > 2.25.1
> > > >
> >
> > --
> > மணிவண்ணன் சதாசிவம்

--
மணிவண்ணன் சதாசிவம்