linux-kernel - Re: [PATCH v7 1/2] PCI: dwc: Implement general suspend/resume functionality for L2/L3 transitions

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Message-ID: <ZMqj/4Yc6U5YqmHJ@lizhi-Precision-Tower-5810>
Date:   Wed, 2 Aug 2023 14:44:52 -0400
From:   Frank Li <Frank.li@....com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     mani@...nel.org, 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, lorenzo.pieralisi@....com,
        lpieralisi@...nel.org, manivannan.sadhasivam@...aro.org,
        minghuan.lian@....com, mingkai.hu@....com, robh+dt@...nel.org,
        roy.zang@....com, shawnguo@...nel.org, zhiqiang.hou@....com
Subject: Re: [PATCH v7 1/2] PCI: dwc: Implement general suspend/resume
 functionality for L2/L3 transitions

On Wed, Aug 02, 2023 at 11:31:38AM -0500, Bjorn Helgaas wrote:
> On Wed, Aug 02, 2023 at 11:57:47AM -0400, Frank Li wrote:
> > Introduce helper function dw_pcie_get_ltssm to retrieve SMLH_LTSS_STATE.
> 
> s/dw_pcie_get_ltssm/dw_pcie_get_ltssm()/
> 
> > Add callback .pme_turn_off and .exit_from_l2 for platform specific PME
> > handling.
> > 
> > Add common dw_pcie_suspend(resume)_noirq() API to avoid duplicated code
> > in dwc pci host controller platform driver.
> > 
> > Typical L2 entry workflow/dw_pcie_suspend_noirq()
> > 
> > 1. Transmit PME turn off signal to PCI devices and wait for PME_To_Ack.
> > 2. Await link entering L2_IDLE state.
> > 
> > Typical L2 exit workflow/dw_pcie_resume_noirq()
> > 
> > 1. Issue exit from L2 command.
> > 2. Reinitialize PCI host.
> > 3. Wait for link to become active.
> > 
> > Signed-off-by: Frank Li <Frank.Li@....com>
> > ---
> >  Change from v6 to v7
> >  - change according to Manivannan's comments.
> >    fix sleep value 100 (should be 1000 for 1ms).
> 
> > +	 * PCI Express Base Specification Rev 4.0 Section 5.3.3.2.1 PME
> > +	 * Synchronization Recommends 1ms to 10ms timeout to check L2 ready.
> > +	 */
> > +	ret = read_poll_timeout(dw_pcie_get_ltssm, val, val == DW_PCIE_LTSSM_L2_IDLE,
> > +				1000, 10000, false, pci);
> 
> Thanks for the spec citation.  Can you please reference the current
> spec, i.e., "PCIe r6.0, sec 5.3.3.2.1".
> 
> s/Recommends/recommends/
> 
> It would really be great to have a #define for this since the bare
> numbers are not very meaningful and they're not specific to DWC so a
> #define would let us find similar situations in other drivers.

how about define as

#define PCI_PME_TO_L2_TIMEOUT 10000

ret = read_poll_timeout(dw_pcie_get_ltssm, val, val == DW_PCIE_LTSSM_L2_IDLE,
                           PCI_PME_TO_L2_TIMEOUT/10, PCI_PME_TO_L2_TIMEOUT, false, pci);

where is good place PCI_PME_TO_L2_TIMEOUT in?

pcie-designware.h or pci.h?

Frank

> 
> Bjorn