Re: [PATCH V3] PCI: imx6: Wait the clocks to stabilize after ref_en

[Bjorn Helgaas <bhelgaas@google.com>]

On Mon, Oct 27, 2014 at 01:17:32PM +0800, Richard Zhu wrote:
> From: Richard Zhu <r65037@freescale.com>
> 
> For boards without a reset GPIO we skip the delay between enabling the
> pcie_ref_clk and touching the RC registers for configuration.
> This hangs the system if there isn't a proper delay to ensure the clocks
> are settled in the DW PCIe core.
> 
> Also iMX6Q always needs an additional 10us delay to make sure the reset
> is propagated through the core, as we don't have an explicitly
> controlled reset input on this SoC.
> 
> Signed-off-by: Richard Zhu <richard.zhu@freescale.com>
> Tested-by: Fabio Estevam <fabio.estevam@freescale.com>
> Acked-by: Lucas Stach <l.stach@pengutronix.de>

I added the regression info to the changelog and applied this to for-linus
for v3.18, thanks!

> ---
>  drivers/pci/host/pci-imx6.c | 13 ++++++++++---
>  1 file changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/pci/host/pci-imx6.c b/drivers/pci/host/pci-imx6.c
> index 233fe8a..eac96fb 100644
> --- a/drivers/pci/host/pci-imx6.c
> +++ b/drivers/pci/host/pci-imx6.c
> @@ -275,15 +275,22 @@ static int imx6_pcie_deassert_core_reset(struct pcie_port *pp)
>  		goto err_pcie;
>  	}
>  
> -	/* allow the clocks to stabilize */
> -	usleep_range(200, 500);
> -
>  	/* power up core phy and enable ref clock */
>  	regmap_update_bits(imx6_pcie->iomuxc_gpr, IOMUXC_GPR1,
>  			IMX6Q_GPR1_PCIE_TEST_PD, 0 << 18);
> +	/*
> +	 * the async reset input need ref clock to sync internally,
> +	 * when the ref clock comes after reset, internal synced
> +	 * reset time is too short , cannot meet the requirement.
> +	 * add one ~10us delay here.
> +	 */
> +	udelay(10);
>  	regmap_update_bits(imx6_pcie->iomuxc_gpr, IOMUXC_GPR1,
>  			IMX6Q_GPR1_PCIE_REF_CLK_EN, 1 << 16);
>  
> +	/* allow the clocks to stabilize */
> +	usleep_range(200, 500);
> +
>  	/* Some boards don't have PCIe reset GPIO. */
>  	if (gpio_is_valid(imx6_pcie->reset_gpio)) {
>  		gpio_set_value(imx6_pcie->reset_gpio, 0);
> -- 
> 1.9.1
>