linux-kernel - Re: [PATCH v5 1/2] PCI: dwc: Implement general suspend/resume functionality for L2/L3 transitionse

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Message-ID: <20230731165457.GA13422@bhelgaas>
Date:   Mon, 31 Jul 2023 11:54:57 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Frank Li <Frank.li@....com>
Cc:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        lorenzo.pieralisi@....com, bhelgaas@...gle.com,
        devicetree@...r.kernel.org, gustavo.pimentel@...opsys.com,
        imx@...ts.linux.dev, kw@...ux.com, leoyang.li@....com,
        linux-arm-kernel@...ts.infradead.org, linux-imx@....com,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        mani@...nel.org, minghuan.lian@....com, mingkai.hu@....com,
        robh+dt@...nel.org, roy.zang@....com, shawnguo@...nel.org,
        zhiqiang.hou@....com
Subject: Re: [PATCH v5 1/2] PCI: dwc: Implement general suspend/resume
 functionality for L2/L3 transitionse

On Fri, Jul 28, 2023 at 11:49:28AM -0400, Frank Li wrote:
> On Fri, Jul 28, 2023 at 09:02:38PM +0530, Manivannan Sadhasivam wrote:
> > On Mon, Jul 24, 2023 at 05:58:29PM -0400, Frank Li wrote:
> > > Introduced helper function dw_pcie_get_ltssm to retrieve SMLH_LTSS_STATE.
> > > Added API pme_turn_off and exit_from_l2 for managing L2/L3 state transitions.
> > > ...

> > > +static void dw_pcie_set_dstate(struct dw_pcie *pci, pci_power_t dstate)
> > > +{
> > > +	u8 offset = dw_pcie_find_capability(pci, PCI_CAP_ID_PM);
> > > +	u16 val;
> > > +
> > > +	val = dw_pcie_readw_dbi(pci, offset + PCI_PM_CTRL);
> > > +	val &= ~PCI_PM_CTRL_STATE_MASK;
> > > +	val |= ((u16 __force)dstate) & PCI_PM_CTRL_STATE_MASK;
> > 
> > Why can't just,
> > 
> > val |= dstate;
> 
> fixed a build warning.
> 
> Closes: https://lore.kernel.org/oe-kbuild-all/202307211904.zExw4Q8H-lkp@intel.com/

This is the sparse warning from the lkp URL:

  sparse warnings: (new ones prefixed by >>)
  >> drivers/pci/controller/dwc/pcie-designware-host.c:824:13: sparse: sparse: invalid assignment: |=
  >> drivers/pci/controller/dwc/pcie-designware-host.c:824:13: sparse:    left side has type unsigned int
  >> drivers/pci/controller/dwc/pcie-designware-host.c:824:13: sparse:    right side has type restricted pci_power_t

We have a zillion of those warnings already (try "make C=2 drivers/pci/").

Personally I think it's better to omit the ugly cast and live with the
warning for now.  Someday somebody will figure a better way to use
pci_power_t that will fix all these warnings at once.  I'd rather wait
for that fix than clutter all the uses with casts like this.

Bjorn