linux-kernel - Re: [PATCH v4 2/3] dwc: PCI: intel: PCIe RC controller driver

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Message-ID: <f74cdada-c58b-7238-9be1-8b001ca1fb84@linux.intel.com>
Date:   Tue, 29 Oct 2019 15:45:56 +0800
From:   Dilip Kota <eswara.kota@...ux.intel.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     jingoohan1@...il.com, gustavo.pimentel@...opsys.com,
        lorenzo.pieralisi@....com, andrew.murray@....com, robh@...nel.org,
        martin.blumenstingl@...glemail.com, linux-pci@...r.kernel.org,
        hch@...radead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, andriy.shevchenko@...el.com,
        cheol.yong.kim@...el.com, chuanhua.lei@...ux.intel.com,
        qi-ming.wu@...el.com
Subject: Re: [PATCH v4 2/3] dwc: PCI: intel: PCIe RC controller driver


On 10/22/2019 9:09 PM, Bjorn Helgaas wrote:
> On Tue, Oct 22, 2019 at 05:07:47PM +0800, Dilip Kota wrote:
>> On 10/22/2019 1:17 AM, Bjorn Helgaas wrote:
>>> On Mon, Oct 21, 2019 at 02:39:19PM +0800, Dilip Kota wrote:
>>>> Add support to PCIe RC controller on Intel Gateway SoCs.
>>>> PCIe controller is based of Synopsys DesignWare pci core.
>>>>
>>>> Intel PCIe driver requires Upconfig support, fast training
>>>> sequence configuration and link speed change. So adding the
>>>> respective helper functions in the pcie DesignWare framework.
>>>> It also programs hardware autonomous speed during speed
>>>> configuration so defining it in pci_regs.h.
>>>>
>>>> +static void intel_pcie_link_setup(struct intel_pcie_port *lpp)
>>>> +{
>>>> +	u32 val;
>>>> +
>>>> +	val = pcie_rc_cfg_rd(lpp, PCIE_CAP_OFST + PCI_EXP_LNKCAP);
>>>> +	lpp->max_speed = FIELD_GET(PCI_EXP_LNKCAP_SLS, val);
>>>> +	lpp->max_width = FIELD_GET(PCI_EXP_LNKCAP_MLW, val);
>>>> +
>>>> +	val = pcie_rc_cfg_rd(lpp, PCIE_CAP_OFST + PCI_EXP_LNKCTL);
>>>> +
>>>> +	val &= ~(PCI_EXP_LNKCTL_LD | PCI_EXP_LNKCTL_ASPMC);
>>>> +	val |= (PCI_EXP_LNKSTA_SLC << 16) | PCI_EXP_LNKCTL_CCC |
>>>> +	       PCI_EXP_LNKCTL_RCB;
>>> PCI_EXP_LNKCTL_CCC is RW.  But doesn't it depend on the components on
>>> both ends of the link?  Do you know what device is at the other end?
>>> I would have assumed that you'd have to start with CCC==0, which
>>> should be most conservative, then set CCC=1 only if you know both ends
>>> have a common clock.
>> PCIe RC and endpoint device are having the common clock so set the CCC=1.
> How do you know what the endpoint device is?  Is this driver only for
> a specific embedded configuration where the endpoint is always
> soldered down?  There's no possibility of this RC being used with a
> connector?
>
> Shouldn't this be either discoverable or configurable via DT or
> something?  pcie_aspm_configure_common_clock() seems to do something
> similar, but I can't really vouch for its correctness.

(sorry for the late reply, i am back today from sick leave)

I see pcie_aspm_configure_common_clock() is getting called during pcie 
root bus bridge scanning and programming the CCC.

So, CCC configuration can be removed here in intel_pcie_link_setup().

Regards,
Dilip

>
> Bjorn