Re: [PATCH V4 27/28] PCI: tegra: Add support for GPIO based PERST#

[Thierry Reding <thierry.reding@gmail.com>]

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On Thu, May 16, 2019 at 11:23:06AM +0530, Manikanta Maddireddy wrote:
> Add support for GPIO based PERST# signal. GPIO number comes from per port
> PCIe device tree node.
> 
> Signed-off-by: Manikanta Maddireddy <mmaddireddy@nvidia.com>
> ---
> V4: Using devm_gpiod_get_from_of_node() to get reset-gpios
> 
> V3: Using helper function to get reset-gpios
> 
> V2: Using standard "reset-gpio" property
> 
>  drivers/pci/controller/pci-tegra.c | 41 +++++++++++++++++++++++++-----
>  1 file changed, 35 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/pci/controller/pci-tegra.c b/drivers/pci/controller/pci-tegra.c
> index 06b99fcbf382..09b4d384ba38 100644
> --- a/drivers/pci/controller/pci-tegra.c
> +++ b/drivers/pci/controller/pci-tegra.c
> @@ -17,6 +17,7 @@
>  #include <linux/debugfs.h>
>  #include <linux/delay.h>
>  #include <linux/export.h>
> +#include <linux/gpio.h>
>  #include <linux/interrupt.h>
>  #include <linux/iopoll.h>
>  #include <linux/irq.h>
> @@ -400,6 +401,8 @@ struct tegra_pcie_port {
>  	unsigned int lanes;
>  
>  	struct phy **phys;
> +
> +	struct gpio_desc *reset_gpiod;

Nit: I'd leave away the "d" at the end there. Or perhaps even the _gpio
suffix entirely. But it's fine either way.

>  };
>  
>  struct tegra_pcie_bus {
> @@ -583,15 +586,23 @@ static void tegra_pcie_port_reset(struct tegra_pcie_port *port)
>  	unsigned long value;
>  
>  	/* pulse reset signal */
> -	value = afi_readl(port->pcie, ctrl);
> -	value &= ~AFI_PEX_CTRL_RST;
> -	afi_writel(port->pcie, value, ctrl);
> +	if (port->reset_gpiod) {
> +		gpiod_set_value(port->reset_gpiod, 0);

So is this actually deasserting the reset pin, or is it asserting a
low-active reset? I think it's the latter, because ...

> +	} else {
> +		value = afi_readl(port->pcie, ctrl);
> +		value &= ~AFI_PEX_CTRL_RST;
> +		afi_writel(port->pcie, value, ctrl);
> +	}
>  
>  	usleep_range(1000, 2000);
>  
> -	value = afi_readl(port->pcie, ctrl);
> -	value |= AFI_PEX_CTRL_RST;
> -	afi_writel(port->pcie, value, ctrl);
> +	if (port->reset_gpiod) {
> +		gpiod_set_value(port->reset_gpiod, 1);

After this the port should be functional, right? I think it'd be better
to reverse the logic here and move the polarity of the GPIO into device
tree. gpiod_set_value() takes care of inverting the level internally if
the GPIO is marked as low-active in DT.

The end result is obviously the same, but it makes the usage much
clearer. If somebody want to write a DT for their board, they will look
at the schematics and see a low-active reset line and may be tempted to
describe it as such in DT, but with your current code that would be
exactly the wrong way around.

> +	} else {
> +		value = afi_readl(port->pcie, ctrl);
> +		value |= AFI_PEX_CTRL_RST;
> +		afi_writel(port->pcie, value, ctrl);
> +	}
>  }
>  
>  static void tegra_pcie_enable_rp_features(struct tegra_pcie_port *port)
> @@ -2238,6 +2249,7 @@ static int tegra_pcie_parse_dt(struct tegra_pcie *pcie)
>  		struct tegra_pcie_port *rp;
>  		unsigned int index;
>  		u32 value;
> +		char *label;
>  
>  		err = of_pci_get_devfn(port);
>  		if (err < 0) {
> @@ -2296,6 +2308,23 @@ static int tegra_pcie_parse_dt(struct tegra_pcie *pcie)
>  		if (IS_ERR(rp->base))
>  			return PTR_ERR(rp->base);
>  
> +		label = kasprintf(GFP_KERNEL, "pex-reset-%u", index);

devm_kasprintf()?

Thierry

> +		if (!label) {
> +			dev_err(dev, "failed to create reset GPIO label\n");
> +			return -ENOMEM;
> +		}
> +
> +		rp->reset_gpiod = devm_gpiod_get_from_of_node(dev, port,
> +							      "reset-gpios", 0,
> +							      GPIOD_OUT_LOW,
> +							      label);
> +		kfree(label);
> +		if (IS_ERR(rp->reset_gpiod)) {
> +			err = PTR_ERR(rp->reset_gpiod);
> +			dev_err(dev, "failed to get reset GPIO: %d\n", err);
> +			return err;
> +		}
> +
>  		list_add_tail(&rp->list, &pcie->ports);
>  	}
>  
> -- 
> 2.17.1
> 

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