Date:   Mon, 9 Jan 2017 12:02:38 -0800
From:   David Daney <ddaney@...iumnetworks.com>
To:     Linus Walleij <linus.walleij@...aro.org>,
        David Daney <ddaney.cavm@...il.com>
CC:     Alexandre Courbot <gnurou@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        David Daney <david.daney@...ium.com>,
        Marc Zyngier <marc.zyngier@....com>
Subject: Re: [PATCH v2 2/3] gpio: Add gpio driver support for ThunderX and
 OCTEON-TX

On 01/09/2017 11:35 AM, Linus Walleij wrote:
> On Sat, Jan 7, 2017 at 12:22 AM, David Daney <ddaney.cavm@...il.com> wrote:
>
>> From: David Daney <david.daney@...ium.com>
>>
>> Cavium ThunderX and OCTEON-TX are arm64 based SoCs.  Add driver for
>> the on-chip GPIO pins.
>>
>> Signed-off-by: David Daney <david.daney@...ium.com>
>
> (...)
>> +config GPIO_THUNDERX
>> +       tristate "Cavium ThunderX/OCTEON-TX GPIO"
>
> Do you really load this as module? OK then...

The driver does work when loaded as a module.  I have tested loading and 
unloading it many times.

>
>> +#include <linux/gpio.h>
>
> No.
> #include <linux/gpio/driver.h>
>
> Nothing else.

Right, I will fix that.

>
>> +#define GLITCH_FILTER_400NS ((4ull << GPIO_BIT_CFG_FIL_SEL_SHIFT) | \
>> +                            (9ull << GPIO_BIT_CFG_FIL_CNT_SHIFT))
>> +
>> +static unsigned int bit_cfg_reg(unsigned int line)
>> +{
>> +       return 8 * line + GPIO_BIT_CFG;
>> +}
>> +
>> +static unsigned int intr_reg(unsigned int line)
>> +{
>> +       return 8 * line + GPIO_INTR;
>> +}
>
> This looks a bit overzealous, but OK.
>
>> +struct thunderx_gpio;
>> +
>> +struct thunderx_irqdev {
>> +       struct thunderx_gpio    *gpio;
>> +       char                    *name;
>> +       unsigned int            line;
>> +};
>> +
>> +struct thunderx_gpio {
>> +       struct gpio_chip        chip;
>> +       u8 __iomem              *register_base;
>> +       struct msix_entry       *msix_entries;
>> +       struct thunderx_irqdev  *irqdev_entries;
>> +       raw_spinlock_t          lock;
>> +       unsigned long           invert_mask[2];
>> +       unsigned long           od_mask[2];
>> +       int                     base_msi;
>> +};
>
> Why can't you just move the thunderx_irqdev fields
> into thunderx_gpio?

There is a variable length array of them.  It is not a single instance 
of the structure.  Same for the msix_entries.

> It will save very little memory for
> non-irq systems, I do not think footprint warrants it.
>
>> +
>> +static bool thunderx_gpio_is_gpio(struct thunderx_gpio *gpio,
>> +                                 unsigned int line)
>> +{
>> +       u64 bit_cfg = readq(gpio->register_base + bit_cfg_reg(line));
>> +       bool rv = (bit_cfg & GPIO_BIT_CFG_PIN_SEL_MASK) == 0;
>> +
>> +       WARN_RATELIMIT(!rv, "Pin %d not available for GPIO\n", line);
>> +
>> +       return rv;
>> +}
>
> Nifty. So this actually has a pin controller back-end?

The hardware does function like a "pin controller"

> I haven't seen the code for that yet, I think.
>
> This seems like a cheap version of
>
> /* External interface to pin control */
> extern int pinctrl_request_gpio(unsigned gpio);
> extern void pinctrl_free_gpio(unsigned gpio);
> extern int pinctrl_gpio_direction_input(unsigned gpio);
> extern int pinctrl_gpio_direction_output(unsigned gpio);
>
> From <linux/pinctrl/consumer.h>
>
> So are you planning pin control support separately in drivers/pinctrl/*
> in the future?

Not at this time.  Currently early boot firmware is programming the pin 
functions, and we don't see a need to move the complexity of pinctrl 
into the kernel, especially as there is not really any ACPI support for 
pinctrl at this point, and we must also support ACPI.

> Maybe some comment to replace this with proper pin control
> in the future is warranted?
>

Good idea.  I will add a comment about this.


>> +static int thunderx_gpio_dir_in(struct gpio_chip *chip, unsigned int line)
>> +{
>> +       struct thunderx_gpio *gpio = container_of(chip, struct thunderx_gpio, chip);
>
> 1. Please use gpiochip_get_data() instead of the container_of() construction,
>    utilized devm_gpiochip_add_data() in your probe() call.
>
> 2. Do not call this local variable "gpio" that is superconfusing, at least call
>     it txgpio or something.
>
> 1 & 2 applies EVERYWHERE in thid driver.

OK, I will make that change for the next revision of the patch set.

>
>> +static void thunderx_gpio_set(struct gpio_chip *chip, unsigned int line,
>> +                             int value)
>> +{
>> +       struct thunderx_gpio *gpio = container_of(chip, struct thunderx_gpio, chip);
>> +       int bank = line / 64;
>> +       int bank_bit = line % 64;
>> +
>> +       void __iomem *reg = gpio->register_base +
>> +               (bank * GPIO_2ND_BANK) + (value ? GPIO_TX_SET : GPIO_TX_CLR);
>> +
>> +       writeq(1ull << bank_bit, reg);
>
> Use this:
>
> #include <linus/bitops.h>
>
> writeq(BIT(bank_bit), reg);
>
> Applies EVERYWHERE you use (1ULL << n)

OK.

>
>> +static int thunderx_gpio_set_single_ended(struct gpio_chip *chip,
>> +                                         unsigned int line,
>> +                                         enum single_ended_mode mode)
>
> Thanks for implementing this properly.
>
>> +       read_bits >>= bank_bit;
>> +
>> +       if (test_bit(line, gpio->invert_mask))
>> +               return !(read_bits & 1);
>> +       else
>> +               return read_bits & 1;
>
> This looks superconvoluted.
>
> Can't you just:
>
> if (test_bit(line, gpio->invert_mask))
>    return !(read_bits & BIT(bank_bit));
> else
>    return !!(read_bits & BIT(bank_bit));
>
> OK maybe not much clearer but seems clearer to me.

As I really dislike the "!!" idiom, would you settle for:

  if (test_bit(line, gpio->invert_mask))
     return (read_bits & BIT(bank_bit)) == 0;
  else
     return (read_bits & BIT(bank_bit)) != 0;

>
>> +static int thunderx_gpio_irq_request_resources(struct irq_data *data)
>> +{
>> +       struct gpio_chip *chip = irq_data_get_irq_chip_data(data);
>> +       struct thunderx_gpio *gpio = container_of(chip, struct thunderx_gpio, chip);
>> +       unsigned int line = data->hwirq;
>> +       struct thunderx_irqdev *irqdev;
>> +       int err;
>> +
>> +       if (!thunderx_gpio_is_gpio(gpio, line))
>> +               return -EIO;
>> +
>> +       irqdev = gpio->irqdev_entries + line;
>> +
>> +       irqdev->gpio = gpio;
>> +       irqdev->line = line;
>> +       irqdev->name = devm_kasprintf(chip->parent, GFP_KERNEL,
>> +                                     "gpio-%d", line + chip->base);
>> +
>> +       writeq(GPIO_INTR_ENA_W1C, gpio->register_base + intr_reg(line));
>> +
>> +       err = devm_request_irq(chip->parent, gpio->msix_entries[line].vector,
>> +                              thunderx_gpio_chain_handler, IRQF_NO_THREAD, irqdev->name, irqdev);
>> +       return err;
>> +}
>> +
>> +static void thunderx_gpio_irq_release_resources(struct irq_data *data)
>> +{
>> +       struct gpio_chip *chip = irq_data_get_irq_chip_data(data);
>> +       struct thunderx_gpio *gpio = container_of(chip, struct thunderx_gpio, chip);
>> +       unsigned int line = data->hwirq;
>> +       struct thunderx_irqdev *irqdev;
>> +
>> +       irqdev = gpio->irqdev_entries + line;
>> +
>> +       /*
>> +        * The request_resources/release_resources functions may be
>> +        * called multiple times in the lifitime of the driver, so we
>> +        * need to clean up the devm_* things to avoid a resource
>> +        * leak.
>> +        */
>> +       devm_free_irq(chip->parent, gpio->msix_entries[line].vector, irqdev);
>> +
>> +       writeq(GPIO_INTR_ENA_W1C, gpio->register_base + intr_reg(line));
>> +
>> +       devm_kfree(chip->parent, irqdev->name);
>> +}
>
> Then just do not use the devm* variants. Explicitly allocate and free instead.
>
> These callbacks should be called on all resources anyways.

Rithe.

>
>> +static void thunderx_gpio_irq_unmask(struct irq_data *data)
>> +{
>> +       struct gpio_chip *chip = irq_data_get_irq_chip_data(data);
>> +       struct thunderx_gpio *gpio = container_of(chip, struct thunderx_gpio, chip);
>> +       unsigned int line = data->hwirq;
>> +
>> +       writeq(GPIO_INTR_ENA_W1S, gpio->register_base + intr_reg(line));
>> +}
>> +
>> +static int thunderx_gpio_irq_set_type(struct irq_data *data,
>> +                                     unsigned int flow_type)
>> +{
>> +       struct gpio_chip *chip = irq_data_get_irq_chip_data(data);
>> +       struct thunderx_gpio *gpio = container_of(chip, struct thunderx_gpio, chip);
>> +       unsigned int line = data->hwirq;
>> +       u64 bit_cfg;
>> +
>> +       irqd_set_trigger_type(data, flow_type);
>> +
>> +       bit_cfg = GLITCH_FILTER_400NS | GPIO_BIT_CFG_INT_EN;
>> +
>> +       if (flow_type & IRQ_TYPE_EDGE_BOTH) {
>> +               irq_set_handler_locked(data, handle_edge_irq);
>> +               bit_cfg |= GPIO_BIT_CFG_INT_TYPE;
>> +       } else {
>> +               irq_set_handler_locked(data, handle_level_irq);
>> +       }
>> +
>> +       raw_spin_lock(&gpio->lock);
>> +       if (flow_type & (IRQ_TYPE_EDGE_FALLING | IRQ_TYPE_LEVEL_LOW)) {
>> +               bit_cfg |= GPIO_BIT_CFG_PIN_XOR;
>> +               set_bit(line, gpio->invert_mask);
>> +       } else {
>> +               clear_bit(line, gpio->invert_mask);
>> +       }
>> +       clear_bit(line, gpio->od_mask);
>> +       writeq(bit_cfg, gpio->register_base + bit_cfg_reg(line));
>> +       raw_spin_unlock(&gpio->lock);
>> +
>> +       return IRQ_SET_MASK_OK;
>> +}
>> +
>> +/*
>> + * Interrupts are chained from underlying MSI-X vectors.  We have
>> + * these irq_chip functions to be able to handle level triggering
>> + * semantics and other acknowledgment tasks associated with the GPIO
>> + * mechanism.
>> + */
>> +static struct irq_chip thunderx_gpio_irq_chip = {
>> +       .name                   = "GPIO",
>> +       .irq_enable             = thunderx_gpio_irq_unmask,
>> +       .irq_disable            = thunderx_gpio_irq_mask,
>> +       .irq_ack                = thunderx_gpio_irq_ack,
>> +       .irq_mask               = thunderx_gpio_irq_mask,
>> +       .irq_mask_ack           = thunderx_gpio_irq_mask_ack,
>> +       .irq_unmask             = thunderx_gpio_irq_unmask,
>> +       .irq_set_type           = thunderx_gpio_irq_set_type,
>> +       .irq_request_resources  = thunderx_gpio_irq_request_resources,
>> +       .irq_release_resources  = thunderx_gpio_irq_release_resources,
>> +       .flags                  = IRQCHIP_SET_TYPE_MASKED
>> +};
>
> This looks wrong.
>
> If you're calling devm_request_irq() on *every* *single* *irq* like you
> do here, you are dealing with a hieararchical irqdomain, not a linear one,
> and GPIOLIB_IRQCHIP may not be used.
>
> Look at drivers/gpio/gpio-xgene-sb.c for inspiration. That is the only
> hierarchical GPIO irqdomain I have right now.
>
> Consult Marc Zyngier's IRQ domain lecture if you have time:
> https://www.youtube.com/watch?v=YE8cRHVIM4E
>
> If you have ideas how to combine hierarchical irqdomain and GPIOLIB_IRQCHIP
> pls help out.
>
>> +       gpio->irqdev_entries = devm_kzalloc(dev,
>> +                                           sizeof(struct thunderx_irqdev) * ngpio,
>> +                                           GFP_KERNEL);
>> +       if (!gpio->irqdev_entries) {
>> +               err = -ENOMEM;
>> +               goto out;
>> +       }
>
> I think this is overkill. Use hierarchical irqdomain.

I will look into it.  I suspect it will require more lines of driver 
code to implement it than what I have here (that does actually work).

Thanks for looking at this,
David

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