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

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Date:   Wed, 2 Aug 2023 11:31:38 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Frank Li <Frank.Li@....com>
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 11:57:47AM -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.

Bjorn