Re: [PATCH 2/3] gpio: Add GPIO support for Broadcom STB SoCs

[Gregory Fong]

Hi Linus,

On Tue, May 12, 2015 at 3:55 AM, Linus Walleij <linus.walleij@xxxxxxxxxx> wrote:
> On Wed, May 6, 2015 at 10:37 AM, Gregory Fong <gregory.0xf0@xxxxxxxxx> wrote:
>
>> This adds support for the GPIO IP "UPG GIO" used on Broadcom STB SoCs
>> (BCM7XXX and some others).  Uses basic_mmio_gpio to instantiate a
>> gpio_chip for each bank.  The driver assumes that it handles the base
>> set of GPIOs on the system and that it can start its numbering sequence
>> from 0, so any GPIO expanders used with it must dynamically assign GPIO
>> numbers after this driver has finished registering its GPIOs.
>>
>> Does not implement the interrupt-controller portion yet, will be done in a
>> future commit.
>>
>> List-usage-fixed-by: Brian Norris <computersforpeace@xxxxxxxxx>
>> Signed-off-by: Gregory Fong <gregory.0xf0@xxxxxxxxx>
>
> (...)
>>  arch/arm/mach-bcm/Kconfig   |    1 +
> (...)
>> --- a/arch/arm/mach-bcm/Kconfig
>> +++ b/arch/arm/mach-bcm/Kconfig
>> @@ -144,6 +144,7 @@ config ARCH_BRCMSTB
>>         select BRCMSTB_GISB_ARB
>>         select BRCMSTB_L2_IRQ
>>         select BCM7120_L2_IRQ
>> +       select ARCH_WANT_OPTIONAL_GPIOLIB
>
> Please remove this from this patch. I don't want to patch around
> in the platforms from the GPIO tree. Take this oneliner through
> ARM SoC.

Will move to a separate patch.

>
>> +config GPIO_BRCMSTB
>> +       tristate "BRCMSTB GPIO support"
>> +       default y if ARCH_BRCMSTB
>> +       depends on OF_GPIO && (ARCH_BRCMSTB || COMPILE_TEST)
>> +       select GPIO_GENERIC
>
> Nice.
>
>> +++ b/drivers/gpio/gpio-brcmstb.c
> (...)
>> +
>> +#include <linux/bitops.h>
>> +#include <linux/gpio.h>
>
> #include <linux/gpio/driver.h>
>
> should be sufficient.

OK.

>
>> +struct brcmstb_gpio_bank {
>> +       struct list_head node;
>> +       int id;
>> +       struct bgpio_chip bgc;
>> +       u32 imask;  /* irq mask shadow register */
>
> Why? Is it a write-only register that can't be read back?

No, that wasn't necessary.  Will change to just read the register.

>
>> +       struct brcmstb_gpio_priv *parent_priv;  /* used in interrupt handler */
>
> ...and this patch does not enable IRQs...

OK, I will move it to the patch that does.

>
>> +struct brcmstb_gpio_priv {
>> +       struct list_head bank_list;
>> +       void __iomem *reg_base;
>> +       int num_banks;
>> +       struct platform_device *pdev;
>> +       int gpio_base;
>
> Usually we don't like it when you hardcode gpio_base, and this
> field should anyway be present inside the bgpio_chip.gc.base
> isn't it?

This was needed to deal with having a single irq_chip shared across
all of the gpio_chips in a GIO block.  You mentioned that this might
not be the Right Way to do this in your reply on the cover page so
I'll try to explain the reasoning better there.

FWIW: yes, this is inside the first bank's bgpio_chip, and it would be
possible to extract that info.  However, since it is used in
- brcmstb_gpio_to_irq
- brcmstb_gpio_hwirq_to_offset
- brcmstb_gpio_irq_bank_handler
- brcmstb_gpio_of_xlate

It seemed like it would be easier to follow if this were just stored
this in the priv struct, even if it is duplication of information.

>
>> +#define GPIO_PER_BANK           32
>> +#define GPIO_BANK(gpio)         ((gpio) >> 5)
>> +/* assumes GPIO_PER_BANK is a multiple of 2 */
>> +#define GPIO_BIT(gpio)          ((gpio) & (GPIO_PER_BANK - 1))
>
> But this macro and GPIO_PER_BANK does not respect the DT binding
> stating the number of used lines.
>
> You need to call these MAX_GPIO_PER_BANK or something.

Will change the name to MAX_GPIO_PER_BANK.

>
>> +static int brcmstb_gpio_probe(struct platform_device *pdev)
>> +{
>> +       struct device *dev = &pdev->dev;
>> +       struct device_node *np = dev->of_node;
>> +       void __iomem *reg_base;
>> +       struct brcmstb_gpio_priv *priv;
>> +       struct resource *res;
>> +       struct property *prop;
>> +       const __be32 *p;
>> +       u32 bank_width;
>> +       int err;
>> +       static int gpio_base;
>> +
>> +       priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
>> +       if (!priv)
>> +               return -ENOMEM;
>> +
>> +       res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
>> +       reg_base = devm_ioremap_resource(dev, res);
>> +       if (IS_ERR(reg_base))
>> +               return PTR_ERR(reg_base);
>> +
>> +       priv->gpio_base = gpio_base;
>> +       priv->reg_base = reg_base;
>> +       priv->pdev = pdev;
>> +
>> +       INIT_LIST_HEAD(&priv->bank_list);
>> +       if (brcmstb_gpio_sanity_check_banks(dev, np, res))
>> +               return -EINVAL;
>> +
>> +       of_property_for_each_u32(np, "brcm,gpio-bank-widths", prop, p,
>> +                       bank_width) {
>> +               struct brcmstb_gpio_bank *bank;
>> +               struct bgpio_chip *bgc;
>> +               struct gpio_chip *gc;
>> +
>> +               bank = devm_kzalloc(dev, sizeof(*bank), GFP_KERNEL);
>> +               if (!bank) {
>> +                       err = -ENOMEM;
>> +                       goto fail;
>> +               }
>> +
>> +               bank->parent_priv = priv;
>> +               bank->id = priv->num_banks;
>> +
>> +               /*
>> +                * Regs are 4 bytes wide, have data reg, no set/clear regs,
>> +                * and direction bits have 0 = output and 1 = input
>> +                */
>> +               bgc = &bank->bgc;
>> +               err = bgpio_init(bgc, dev, 4,
>> +                               reg_base + GIO_DATA(bank->id),
>> +                               NULL, NULL, NULL,
>> +                               reg_base + GIO_IODIR(bank->id), 0);
>> +               if (err) {
>> +                       dev_err(dev, "bgpio_init() failed\n");
>> +                       goto fail;
>> +               }
>> +
>> +               gc = &bgc->gc;
>> +               gc->of_node = np;
>> +               gc->owner = THIS_MODULE;
>> +               gc->label = np->full_name;
>> +               gc->base = gpio_base;
>
> I strongly suggest that you try using -1 as base here instead
> for dynamic assignment of GPIO numbers.

That is what I did originally.  However, this results in a very
unpleasant numbering scheme, at least as currently implemented.

When -1 is base, as you know, numbering goes descending from 255
(IIRC).  Right now I'm using the of_property_for_each_u32 loop over
bank widths to go through the banks.  To keep the example
straightforward, let's pretend our GIO block only has two banks.
Here's how they're arranged:

bank 0: starts at 0xf040a700, contains GPIOs 0-31
bank 1: starts at 0xf040a720, contains GPIOs 32-63

Right now, with -1 as base, calling gpiochip_add() inside of that loop
will results in them getting this numbering:

bank 0: linux GPIOs 224-255
bank 1: linux GPIOs 192-223

which has the obvious downside that the ordering doesn't at all match
the hardware, making it completely unintuitive for anyone using the
(admittedly quite awful) sysfs interface.

Looking at this now, I think I could just add another loop afterward
to do the gpiochip_add()'s in reverse order, resulting in the
numbering ascending with banks as expected.  Does this seem sensible?

>
>> +               gc->of_gpio_n_cells = 2;
>> +               gc->of_xlate = brcmstb_gpio_of_xlate;
>> +
>> +               if (bank_width <= 0 || bank_width > GPIO_PER_BANK) {
>> +                       gc->ngpio = GPIO_PER_BANK;
>> +                       dev_warn(dev, "Invalid bank width %d, assume %d\n",
>> +                                       bank_width, gc->ngpio);
>
> I wonder if this should not simply return an error.
> If that number is wrong the DTS is completely screwed up.

You're right, probably better to have that be an error.  Will change that.

>
>> +               } else {
>> +                       gc->ngpio = bank_width;
>> +               }
>> +
>> +               bank->imask =
>> +                       bgc->read_reg(reg_base + GIO_MASK(bank->id));
>
> And this mask also mask the unused pins as GIO_MASK()
> does not respect bank_width.

I'll be getting rid of imask anyway as you suggested.  But since you
mentioned it, I just realized that the register specification says
that reads of the reserved bits can return an unknown value but writes
of those bits should be 0.  While in practice it doesn't seem to cause
any problems, I'll change that anyway just to be safe.

>
>> +               err = gpiochip_add(gc);
>> +               if (err) {
>> +                       dev_err(dev, "Could not add gpiochip for bank %d\n",
>> +                                       bank->id);
>> +                       goto fail;
>> +               }
>> +               gpio_base += gc->ngpio;
>
> This complicates things. Use -1 as base for dynamic assignment
> of GPIO numbers.

(this was covered above)

Thanks for the review,
Gregory
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