linux-kernel - Re: [PATCH] pcie-xilinx: Support reset GPIO and wait for link-up status

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Message-ID: <vazbdawfo4jnct4rdokknxwvknespcf33jzrmobsnecbxnrbjn@kbvxvhrow4fn>
Date: Mon, 24 Mar 2025 13:19:47 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Mike Looijmans <mike.looijmans@...ic.nl>
Cc: linux-pci@...r.kernel.org, Bjorn Helgaas <bhelgaas@...gle.com>, 
	Krzysztof Wilczyński <kw@...ux.com>, Lorenzo Pieralisi <lpieralisi@...nel.org>, 
	Michal Simek <michal.simek@....com>, Rob Herring <robh@...nel.org>, 
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] pcie-xilinx: Support reset GPIO and wait for link-up
 status

On Fri, Mar 14, 2025 at 03:59:02PM +0100, Mike Looijmans wrote:
> Support providing the PERST reset signal through a devicetree binding.

Where is the bindings change?

> Thus the system no longer relies on external components to perform the
> bus reset.
> 

There is a similar series for the CPM controller:
https://lore.kernel.org/linux-pci/20250318092648.2298280-1-sai.krishna.musham@amd.com/

Please take a look for reference.

> When the driver loads, the transceiver may still be in the state of
> setting up a link. Wait for that to complete before continuing. This
> fixes that the PCIe core does not work when loading the PL bitstream
> from userspace. There's only milliseconds between the FPGA boot and the
> core initializing in that case, and the link won't be up yet. The design
> works when the FPGA was programmed in the bootloader, as that will give
> the system hundreds of milliseconds to boot.
> 
> As the PCIe spec mentions about 120 ms time to establish a link, we'll
> allow up to 200ms before giving up.
> 

This should be a separate change/patch.

> Signed-off-by: Mike Looijmans <mike.looijmans@...ic.nl>
> ---
> 
>  drivers/pci/controller/pcie-xilinx.c | 25 ++++++++++++++++++++++++-
>  1 file changed, 24 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/controller/pcie-xilinx.c b/drivers/pci/controller/pcie-xilinx.c
> index 0b534f73a942..cd09deba0ddc 100644
> --- a/drivers/pci/controller/pcie-xilinx.c
> +++ b/drivers/pci/controller/pcie-xilinx.c
> @@ -15,8 +15,10 @@
>  #include <linux/irqdomain.h>
>  #include <linux/kernel.h>
>  #include <linux/init.h>
> +#include <linux/iopoll.h>
>  #include <linux/msi.h>
>  #include <linux/of_address.h>
> +#include <linux/of_gpio.h>
>  #include <linux/of_pci.h>
>  #include <linux/of_platform.h>
>  #include <linux/of_irq.h>
> @@ -126,6 +128,14 @@ static inline bool xilinx_pcie_link_up(struct xilinx_pcie *pcie)
>  		XILINX_PCIE_REG_PSCR_LNKUP) ? 1 : 0;
>  }
>  
> +static int xilinx_pci_wait_link_up(struct xilinx_pcie *pcie)
> +{
> +	u32 val;
> +
> +	return readl_poll_timeout(pcie->reg_base + XILINX_PCIE_REG_PSCR, val,
> +			(val & XILINX_PCIE_REG_PSCR_LNKUP), 2000, 200000);
> +}
> +
>  /**
>   * xilinx_pcie_clear_err_interrupts - Clear Error Interrupts
>   * @pcie: PCIe port information
> @@ -492,8 +502,21 @@ static int xilinx_pcie_init_irq_domain(struct xilinx_pcie *pcie)
>  static void xilinx_pcie_init_port(struct xilinx_pcie *pcie)
>  {
>  	struct device *dev = pcie->dev;
> +	struct gpio_desc *perst_gpio;
> +
> +	perst_gpio = devm_gpiod_get_optional(dev, "reset", GPIOD_OUT_HIGH);
> +	if (IS_ERR(perst_gpio)) {
> +		dev_err(dev, "gpio request failed: %d\n", PTR_ERR(perst_gpio));
> +		perst_gpio = NULL;

No. If the GPIO is defined in DT and there is a problem in acquiring it, you
should return the error.

> +	}
> +
> +	if (perst_gpio) {

This check is not needed as gpiod_set_value_cansleep() can accept NULL.

- Mani

-- 
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