linux-kernel - Re: [PATCH v6 4/5] PCI: add PCI controller for keystone PCIe h/w

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Date:	Mon, 21 Jul 2014 10:44:28 +0900
From:	Jingoo Han <jg1.han@...sung.com>
To:	'Murali Karicheri' <m-karicheri2@...com>,
	'Rob Herring' <robherring2@...il.com>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	'Russell King' <linux@....linux.org.uk>,
	'Grant Likely' <grant.likely@...aro.org>,
	'Rob Herring' <robh+dt@...nel.org>,
	'Mohit Kumar' <mohit.kumar@...com>,
	'Bjorn Helgaas' <bhelgaas@...gle.com>,
	'Pratyush Anand' <pratyush.anand@...com>,
	'Richard Zhu' <r65037@...escale.com>,
	'Kishon Vijay Abraham I' <kishon@...com>,
	'Marek Vasut' <marex@...x.de>, 'Arnd Bergmann' <arnd@...db.de>,
	'Pawel Moll' <pawel.moll@....com>,
	'Mark Rutland' <mark.rutland@....com>,
	'Ian Campbell' <ijc+devicetree@...lion.org.uk>,
	'Kumar Gala' <galak@...eaurora.org>,
	'Randy Dunlap' <rdunlap@...radead.org>,
	'Jingoo Han' <jg1.han@...sung.com>
Subject: Re: [PATCH v6 4/5] PCI: add PCI controller for keystone PCIe h/w

On Saturday, July 19, 2014 5:29 AM, Murali Karicheri wrote:
> On 07/18/2014 03:31 PM, Rob Herring wrote:
> > On Fri, Jul 18, 2014 at 10:14 AM, Murali Karicheri<m-karicheri2@...com>  wrote:
> --- Cut ---
> >> +
> >> +Optional properties:-
> >> +       phys: phandle to Generic Keystone SerDes phy for PCI
> >> +       phy-names: name of the Generic Keystine SerDes phy for PCI
> >> +         - If boot loader already does PCI link establishment, then phys and
> >> +           phy-names shouldn't be present.
> >> +       ti,enable-linktrain - Enable Link training.
> >> +         - If boot loader already does PCI link establishment, then this
> >> +           shouldn't be present.
> >
> > Can't you read from the h/w if the link is trained?

I agree with Rob Herring's suggestion.

> 
> Yes.
> 
> There are customers who use this driver with PCI Link setup done in the
> boot loader. This property tells the driver to bypass Link setup
> procedure in that case. Is this undesirable and if so. how other
> platforms handle it? Check first if link is trained or start the link
> setup procedure? Let me know. If this is fine, please provide your Ack.

Please, check the following code of Exynos PCIe diver.

./drivers/pci/host/pci-exynos.c

static int exynos_pcie_establish_link(struct pcie_port *pp)
{
	struct exynos_pcie *exynos_pcie = to_exynos_pcie(pp);
	void __iomem *elbi_base = exynos_pcie->elbi_base;
	void __iomem *pmu_base = exynos_pcie->pmu_base;

	if (dw_pcie_link_up(pp)) {
		dev_err(pp->dev, "Link already up\n");
		return 0;
	}
	.....

In the case of Exynos PCIe, the Exynos PCIe driver checks the
h/w bit such as PCIE_ELBI_LTSSM_ENABLE bit of PCIE_ELBI_RDLH_LINKUP
offset register.

If the link is already set up by the boot loader or other reasons,
the driver will skip some initialization codes.

The first step is that you find such h/w bit for checking link up.
If so, please add the code for skipping, when the link is already
set up.

Best regards,
Jingoo Han

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