linux-kernel - Re: [PATCH v3 2/6] PCI: imx6: Toggle the cold reset for i.MX95 PCIe

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Message-ID: <fatfobrf53l3ngps3rl67gayhnlsqncgd2tabgcspac3n3o4xt@a4yrmtvaitai>
Date: Wed, 2 Apr 2025 12:06:29 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Richard Zhu <hongxing.zhu@....com>
Cc: frank.li@....com, l.stach@...gutronix.de, lpieralisi@...nel.org, 
	kw@...ux.com, robh@...nel.org, bhelgaas@...gle.com, shawnguo@...nel.org, 
	s.hauer@...gutronix.de, kernel@...gutronix.de, festevam@...il.com, 
	linux-pci@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, imx@...ts.linux.dev, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/6] PCI: imx6: Toggle the cold reset for i.MX95 PCIe

On Fri, Mar 28, 2025 at 11:02:09AM +0800, Richard Zhu wrote:
> Add the cold reset toggle for i.MX95 PCIe to align PHY's power up sequency.

What do you mean by 'cold' reset? Is it 'core' reset? I see both terminologies
used in the code.

> 
> Signed-off-by: Richard Zhu <hongxing.zhu@....com>
> ---
>  drivers/pci/controller/dwc/pci-imx6.c | 42 +++++++++++++++++++++++++++
>  1 file changed, 42 insertions(+)
> 
> diff --git a/drivers/pci/controller/dwc/pci-imx6.c b/drivers/pci/controller/dwc/pci-imx6.c
> index 57aa777231ae..6051b3b5928f 100644
> --- a/drivers/pci/controller/dwc/pci-imx6.c
> +++ b/drivers/pci/controller/dwc/pci-imx6.c
> @@ -71,6 +71,9 @@
>  #define IMX95_SID_MASK				GENMASK(5, 0)
>  #define IMX95_MAX_LUT				32
>  
> +#define IMX95_PCIE_RST_CTRL			0x3010
> +#define IMX95_PCIE_COLD_RST			BIT(0)
> +
>  #define to_imx_pcie(x)	dev_get_drvdata((x)->dev)
>  
>  enum imx_pcie_variants {
> @@ -773,6 +776,43 @@ static int imx7d_pcie_core_reset(struct imx_pcie *imx_pcie, bool assert)
>  	return 0;
>  }
>  
> +static int imx95_pcie_core_reset(struct imx_pcie *imx_pcie, bool assert)
> +{
> +	u32 val;
> +
> +	if (assert) {
> +		/*
> +		 * From i.MX95 PCIe PHY perspective, the COLD reset toggle
> +		 * should be complete after power-up by the following sequence.
> +		 *                 > 10us(at power-up)
> +		 *                 > 10ns(warm reset)
> +		 *               |<------------>|
> +		 *                ______________
> +		 * phy_reset ____/              \________________
> +		 *                                   ____________
> +		 * ref_clk_en_______________________/
> +		 * Toggle COLD reset aligned with this sequence for i.MX95 PCIe.
> +		 */
> +		regmap_set_bits(imx_pcie->iomuxc_gpr, IMX95_PCIE_RST_CTRL,
> +				IMX95_PCIE_COLD_RST);

Is this really COLD reset? Or CORE reset?

> +		/*
> +		 * To make sure delay enough time, do regmap_read_bypassed
> +		 * before udelay(). Since udelay() might not use MMIO, and cause
> +		 * delay time less than setting value.
> +		 */

This comment could be rephrased:

		/*
		 * Make sure the write to IMX95_PCIE_RST_CTRL is flushed to the
		 * hardware by doing a read. Otherwise, there is no guarantee
		 * that the write has reached the hardware before udelay().
		 */

- Mani

-- 
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