linux-kernel - Re: [PATCH v4 4/5] PCI: imx6: Convert to agnostic GPIO API

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Message-ID: <ZjxQE8h0-BABxybu@surfacebook.localdomain>
Date: Thu, 9 May 2024 07:24:51 +0300
From: Andy Shevchenko <andy.shevchenko@...il.com>
To: Hongxing Zhu <hongxing.zhu@....com>
Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
	Frank Li <frank.li@....com>,
	Krzysztof Wilczy��ski <kwilczynski@...nel.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"imx@...ts.linux.dev" <imx@...ts.linux.dev>,
	"linux-amlogic@...ts.infradead.org" <linux-amlogic@...ts.infradead.org>,
	"linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	Vignesh Raghavendra <vigneshr@...com>,
	Siddharth Vadapalli <s-vadapalli@...com>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczy��ski <kw@...ux.com>,
	Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
	Lucas Stach <l.stach@...gutronix.de>,
	Shawn Guo <shawnguo@...nel.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Pengutronix Kernel Team <kernel@...gutronix.de>,
	Fabio Estevam <festevam@...il.com>, Yue Wang <yue.wang@...ogic.com>,
	Neil Armstrong <neil.armstrong@...aro.org>,
	Kevin Hilman <khilman@...libre.com>,
	Jerome Brunet <jbrunet@...libre.com>,
	Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
	Xiaowei Song <songxiaowei@...ilicon.com>,
	Binghui Wang <wangbinghui@...ilicon.com>,
	Thierry Reding <thierry.reding@...il.com>,
	Jonathan Hunter <jonathanh@...dia.com>,
	Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
	Pali Rohár <pali@...nel.org>,
	Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [PATCH v4 4/5] PCI: imx6: Convert to agnostic GPIO API

Thu, May 09, 2024 at 01:24:45AM +0000, Hongxing Zhu kirjoitti:
> > -----Original Message-----
> > From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> > Sent: 2024年5月6日 22:21

..

> > -	imx6_pcie->gpio_active_high = of_property_read_bool(node,
> > -						"reset-gpio-active-high");
> > -	if (gpio_is_valid(imx6_pcie->reset_gpio)) {
> > -		ret = devm_gpio_request_one(dev, imx6_pcie->reset_gpio,
> > -				imx6_pcie->gpio_active_high ?
> > -					GPIOF_OUT_INIT_HIGH :
> > -					GPIOF_OUT_INIT_LOW,
> > -				"PCIe reset");
> > -		if (ret) {
> > -			dev_err(dev, "unable to get reset gpio\n");
> > -			return ret;
> > -		}
> > -	} else if (imx6_pcie->reset_gpio == -EPROBE_DEFER) {
> > -		return imx6_pcie->reset_gpio;
> > -	}

> Please correct me if my understand is wrong.
> The "reset-gpio-active-high" property is added for some buggy board designs.
> On these buggy boards, the reset gpio is active high.

This is my understanding too.

> In the other words, the PERST# is active and remote endpoint device would
> be in reset stat when this gpio is high on these buggy boards.

Yes.

> I'm afraid that the PCIe would be broken on these boards, If these codes
>  are removed totally,

No. Linus W. explained in the previous version review round how it's supposed
to work.

> and toggle the reset GPIO pin like below.
> ...
> gpio_set_value_cansleep(imx6_pcie->reset_gpio, 0);
> msleep(100);
> gpio_set_value_cansleep(imx6_pcie->reset_gpio, 1);
> ...

It's not the code that this patch adds. I'm not sure if I understand starting
from here what you mean.

> By the way, this reset GPIO pin should be high at end in
> imx6_pcie_deassert_core_reset() if the imx6_pcie->gpio_active_high is zero. 

This seems a terminology mixup. You probably meant "inactive".
And this is exactly the case with this patch.

If you start thinking in terms of "active"/"inactive" you will see that there
is no contradiction and no behaviour change. The quirk itself is located in
gpiolib-of.c..

-- 
With Best Regards,
Andy Shevchenko