linux-kernel - Re: [PATCH 2/2] PCI: mvebu: switch to using gpiod API

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Date:   Tue, 6 Sep 2022 14:52:42 -0700
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Pali Rohár <pali@...nel.org>
Cc:     Shawn Guo <shawn.guo@...aro.org>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <brgl@...ev.pl>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] PCI: mvebu: switch to using gpiod API

On Tue, Sep 06, 2022 at 11:41:14PM +0200, Pali Rohár wrote:
> On Tuesday 06 September 2022 14:26:32 Dmitry Torokhov wrote:
> > Hi Pali,
> > 
> > On Tue, Sep 06, 2022 at 11:16:28PM +0200, Pali Rohár wrote:
> > > Hello!
> > > 
> > > On Tuesday 06 September 2022 13:43:01 Dmitry Torokhov wrote:
> > > > This patch switches the driver away from legacy gpio/of_gpio API to
> > > > gpiod API, and removes use of of_get_named_gpio_flags() which I want to
> > > > make private to gpiolib.
> > > 
> > > There are many pending pci-mvebu.c patches waiting for review and merge,
> > > so I would suggest to wait until all other mvebu patches are processed
> > > and then process this one... longer waiting period :-(
> > 
> > OK, it is not super urgent. OTOH it is a very simple patch :)
> 
> In the worst case, I will take it into my pending list of pci-mvebu.c
> patches, so it would not be lost. Just yesterday I collected patches and
> created pending list:
> https://git.kernel.org/pub/scm/linux/kernel/git/pali/linux.git/log/?h=pci-mvebu-pending
> 
> > > 
> > > > Signed-off-by: Dmitry Torokhov <dmitry.torokhov@...il.com>
> > > > ---
> > > >  drivers/pci/controller/pci-mvebu.c | 48 +++++++++---------------------
> > > >  1 file changed, 14 insertions(+), 34 deletions(-)
> > > > 
> > > > diff --git a/drivers/pci/controller/pci-mvebu.c b/drivers/pci/controller/pci-mvebu.c
> > > > index 1ced73726a26..a54beb8f611c 100644
> > > > --- a/drivers/pci/controller/pci-mvebu.c
> > > > +++ b/drivers/pci/controller/pci-mvebu.c
> > > > @@ -11,14 +11,13 @@
> > > >  #include <linux/bitfield.h>
> > > >  #include <linux/clk.h>
> > > >  #include <linux/delay.h>
> > > > -#include <linux/gpio.h>
> > > > +#include <linux/gpio/consumer.h>
> > > >  #include <linux/init.h>
> > > >  #include <linux/mbus.h>
> > > >  #include <linux/slab.h>
> > > >  #include <linux/platform_device.h>
> > > >  #include <linux/of_address.h>
> > > >  #include <linux/of_irq.h>
> > > > -#include <linux/of_gpio.h>
> > > >  #include <linux/of_pci.h>
> > > >  #include <linux/of_platform.h>
> > > >  
> > > > @@ -1261,9 +1260,8 @@ static int mvebu_pcie_parse_port(struct mvebu_pcie *pcie,
> > > >  	struct mvebu_pcie_port *port, struct device_node *child)
> > > >  {
> > > >  	struct device *dev = &pcie->pdev->dev;
> > > > -	enum of_gpio_flags flags;
> > > >  	u32 slot_power_limit;
> > > > -	int reset_gpio, ret;
> > > > +	int ret;
> > > >  	u32 num_lanes;
> > > >  
> > > >  	port->pcie = pcie;
> > > > @@ -1327,40 +1325,22 @@ static int mvebu_pcie_parse_port(struct mvebu_pcie *pcie,
> > > >  			 port->name, child);
> > > >  	}
> > > >  
> > > > -	reset_gpio = of_get_named_gpio_flags(child, "reset-gpios", 0, &flags);
> > > > -	if (reset_gpio == -EPROBE_DEFER) {
> > > > -		ret = reset_gpio;
> > > > +	port->reset_name = devm_kasprintf(dev, GFP_KERNEL, "%s-reset",
> > > > +					  port->name);
> > > > +	if (!port->reset_name) {
> > > > +		ret = -ENOMEM;
> > > >  		goto err;
> > > >  	}
> > > >  
> > > > -	if (gpio_is_valid(reset_gpio)) {
> > > > -		unsigned long gpio_flags;
> > > > -
> > > > -		port->reset_name = devm_kasprintf(dev, GFP_KERNEL, "%s-reset",
> > > > -						  port->name);
> > > > -		if (!port->reset_name) {
> > > > -			ret = -ENOMEM;
> > > > +	port->reset_gpio = devm_fwnode_gpiod_get(dev, of_fwnode_handle(child),
> > > > +						 "reset", GPIOD_OUT_HIGH,
> > > 
> > > What does it mean that there is a new GPIOD_OUT_HIGH flag passed to the
> > > devm_fwnode_gpiod_get() function?
> > 
> > This means that we drive the line as "active" as soon as we successfully
> > grab GPIO. This is the same as we had with devm_gpio_request_one(), but
> 
> Ah :-( Another thing to fix. Driver should not change the signal line at
> this stage, but only when it is explicitly asked - at later stage. Some
> PCIe card do not like flipping reset line too quick. I see this fix

As far as I can see the driver has a delay of 100 usec before releasing
reset line, plus additional delay for post-reset. Is this really not
sufficient?

> would not be such easy as during startup we need to reset endpoint card.
> Normally just putting it from reset, but if card was not reset state
> prior probing driver then it is needed to first put it into reset...
> 
> I would fix it this issue after your patch is merged to prevent any
> other merge conflicts.
> 
> How to tell devm_fwnode_gpiod_get() function that caller is not
> interested in changing signal line? Just by changing GPIOD_OUT_HIGH to 0?

I think there are 2 options:

1. Start with GPIOD_OUT_LOW (i.e. reset is explicitly deasserted), and
then in powerup/powerdown you do explicit on/off transitions with proper
timings.

2. Start with GPIOD_ASIS (i.e. do not configure line at all), and then
when powering up you need

	gpiod_direction_output(port->reset_gpio, GPIOD_OUT_HIGH);

on the first invocation (and you can skip call to
gpiod_set_value_cansleep(port->reset_gpio, 1) in that case).

> 
> > we do not need to figure out actual polarity.
> > 
> > > 
> > > > +						 port->name);
> > > > +	ret = PTR_ERR_OR_ZERO(port->reset_gpio);
> > > > +	if (ret) {
> > > > +		if (ret	!= -ENOENT)
> 
> Just one check, I think that between "ret" and "!=" is TAB instead of
> space. But I'm not sure if it was mangled by email client or of there is
> really TAB.

Ah, indeed, sorry about that.

> 
> > > >  			goto err;
> > > > -		}
> > > > -
> > > > -		if (flags & OF_GPIO_ACTIVE_LOW) {
> > > > -			dev_info(dev, "%pOF: reset gpio is active low\n",
> > > > -				 child);
> > > > -			gpio_flags = GPIOF_ACTIVE_LOW |
> > > > -				     GPIOF_OUT_INIT_LOW;
> > > > -		} else {
> > > > -			gpio_flags = GPIOF_OUT_INIT_HIGH;
> > > > -		}
> > > > -
> > > > -		ret = devm_gpio_request_one(dev, reset_gpio, gpio_flags,
> > > > -					    port->reset_name);
> > > > -		if (ret) {
> > > > -			if (ret == -EPROBE_DEFER)
> > > > -				goto err;
> > > > -			goto skip;
> > > > -		}
> > > > -
> > > > -		port->reset_gpio = gpio_to_desc(reset_gpio);
> > > > +		/* reset gpio is optional */
> > > > +		port->reset_gpio = NULL;
> > > 
> > > Maybe you can also release port->reset_name as it is not used at this
> > > stage?
> > 
> > OK, I figured it was just a few bytes, but sure, I'll add devm_kfree().
> > 
> > Thanks for the review.
> > 
> > -- 
> > Dmitry

-- 
Dmitry