linux-kernel - Re: [PATCH] imx6 PCI Host initialisation order

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Date:	Mon, 8 Sep 2014 10:51:06 -0600
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Shawn Guo <shawn.guo@...escale.com>
Cc:	Raymond van der Rots <raymond@...ctrocompaniet.no>,
	Zhu Richard-R65037 <r65037@...escale.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Lucas Stach <l.stach@...gutronix.de>,
	Tim Harvey <tharvey@...eworks.com>
Subject: Re: [PATCH] imx6 PCI Host initialisation order

On Mon, Sep 8, 2014 at 5:28 AM, Shawn Guo <shawn.guo@...escale.com> wrote:
> Hi Raymond,
>
> It seems that there is already a similar patch [1] from Tim floating
> on the list.
>
> Shawn
>
> [1] http://www.spinics.net/lists/linux-pci/msg33520.html

Yes.  MAINTAINERS lists Richard Zhu <r65037@...escale.com> and Shawn
Guo <shawn.guo@...escale.com> (hi Shawn :)) as the caretakers for
pci-imx6.c.  Neither has acked it yet, and Richard asked for a comment
update, which I haven't seen yet.  So I haven't applied it yet.

> On Mon, Sep 08, 2014 at 11:10:37AM +0200, Raymond van der Rots wrote:
>> Hi,
>>
>> The imx6dl on our hardware board frequently had problems bringing up the PCI link, with or without peripherals connected. I found these issues to be due to the initialisation order of the PCI Host.
>>
>> The host driver first enables the phy, and then enables its clocks. However, according to the reference manual (IMX6SDLRM, page 2033):
>> > The phy_ref_ssp_en signal must remain deasserted until the reference clock is running at the appropriate frequency, at which point phy_ref_ssp_en can be asserted.
>>
>>
>> Which implies that the clocks should be brought up first, after which the peripheral should be enabled.
>> This patch changes that initialisation order.
>>
>> I do not have other hardware with an imx6dl, so this patch has only been tested on our board. Could someone confirm that this is more technically correct or improves behaviour?
>>
>> Signed-off-by: Raymond van der Rots <raymond@...ctrocompaniet.no>
>> ---
>> diff --git a/drivers/pci/host/pci-imx6.c b/drivers/pci/host/pci-imx6.c
>> index a568efa..17c35b4 100644
>> --- a/drivers/pci/host/pci-imx6.c
>> +++ b/drivers/pci/host/pci-imx6.c
>> @@ -228,11 +228,6 @@ static int imx6_pcie_deassert_core_reset(struct pcie_port *pp)
>>       struct imx6_pcie *imx6_pcie = to_imx6_pcie(pp);
>>       int ret;
>>
>> -     regmap_update_bits(imx6_pcie->iomuxc_gpr, IOMUXC_GPR1,
>> -                     IMX6Q_GPR1_PCIE_TEST_PD, 0 << 18);
>> -     regmap_update_bits(imx6_pcie->iomuxc_gpr, IOMUXC_GPR1,
>> -                     IMX6Q_GPR1_PCIE_REF_CLK_EN, 1 << 16);
>> -
>>       ret = clk_prepare_enable(imx6_pcie->pcie_phy);
>>       if (ret) {
>>               dev_err(pp->dev, "unable to enable pcie_phy clock\n");
>> @@ -254,6 +249,11 @@ static int imx6_pcie_deassert_core_reset(struct pcie_port *pp)
>>       /* allow the clocks to stabilize */
>>       usleep_range(200, 500);
>>
>> +     regmap_update_bits(imx6_pcie->iomuxc_gpr, IOMUXC_GPR1,
>> +                     IMX6Q_GPR1_PCIE_TEST_PD, 0 << 18);
>> +     regmap_update_bits(imx6_pcie->iomuxc_gpr, IOMUXC_GPR1,
>> +                     IMX6Q_GPR1_PCIE_REF_CLK_EN, 1 << 16);
>> +
>>       /* Some boards don't have PCIe reset GPIO. */
>>       if (gpio_is_valid(imx6_pcie->reset_gpio)) {
>>               gpio_set_value(imx6_pcie->reset_gpio, 0);
>>
>>
--
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