linux-kernel - Re: [PATCH v2 3/3] dwc: PCI: intel: Intel PCIe RC controller driver

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Date:   Thu, 29 Aug 2019 23:01:22 +0200
From:   Martin Blumenstingl <martin.blumenstingl@...glemail.com>
To:     Kishon Vijay Abraham I <kishon@...com>
Cc:     "Chuan Hua, Lei" <chuanhua.lei@...ux.intel.com>,
        eswara.kota@...ux.intel.com, andriy.shevchenko@...el.com,
        cheol.yong.kim@...el.com, devicetree@...r.kernel.org,
        gustavo.pimentel@...opsys.com, hch@...radead.org,
        jingoohan1@...il.com, linux-kernel@...r.kernel.org,
        linux-pci@...r.kernel.org, qi-ming.wu@...el.com
Subject: Re: [PATCH v2 3/3] dwc: PCI: intel: Intel PCIe RC controller driver

Hi Kishon,

On Thu, Aug 29, 2019 at 7:10 AM Kishon Vijay Abraham I <kishon@...com> wrote:
[...]
> The PCI EXPRESS CARD ELECTROMECHANICAL SPECIFICATION defines the Power
> Sequencing and Reset Signal Timings in Table 2-4. Please also refer Figure
> 2-10: Power Up of the CEM.
>
> ╔═════════════╤══════════════════════════════════════╤═════╤═════╤═══════╗
> ║ Symbol      │ Parameter                            │ Min │ Max │ Units ║
> ╠═════════════╪══════════════════════════════════════╪═════╪═════╪═══════╣
> ║ T PVPERL    │ Power stable to PERST# inactive      │ 100 │     │ ms    ║
> ╟─────────────┼──────────────────────────────────────┼─────┼─────┼───────╢
> ║ T PERST-CLK │ REFCLK stable before PERST# inactive │ 100 │     │ μs    ║
> ╟─────────────┼──────────────────────────────────────┼─────┼─────┼───────╢
> ║ T PERST     │ PERST# active time                   │ 100 │     │ μs    ║
> ╟─────────────┼──────────────────────────────────────┼─────┼─────┼───────╢
> ║ T FAIL      │ Power level invalid to PERST# active │     │ 500 │ ns    ║
> ╟─────────────┼──────────────────────────────────────┼─────┼─────┼───────╢
> ║ T WKRF      │ WAKE# rise – fall time               │     │ 100 │ ns    ║
> ╚═════════════╧══════════════════════════════════════╧═════╧═════╧═══════╝
>
> In my code I used T PERST-CLK (i.e REFCLK stable before PERST# inactive).
> REFCLK to the card is enabled as part of PHY enable and then wait for 100μs
> before making PERST# inactive.
>
> Power to the device is given during board power up and the assumption here is
> it will take more the 100ms for the probe to be invoked after board power up
> (i.e after ROM, bootloaders and linux kernel). But if you have a regulator that
> is enabled in PCI probe, then T PVPERL (100ms) should also used in probe.
thank you for this detailed overview and for the explanation about the
assumptions you made (and why)


Martin