Re: [PATCH v4 03/10] gpiolib: implement low-level, shared GPIO support

Jon Hunter
2026-03-12T07:29:00Z

On 11/03/2026 20:14, Andy Shevchenko wrote:
> On Wed, Mar 11, 2026 at 8:38 PM Jon Hunter <jonathanh@nvidia.com> wrote:
>> On 12/11/2025 13:55, Bartosz Golaszewski wrote:
>
> ...
>
>> On Tegra234, the main gpio controller has a total of 164 GPIOs (see
>> the tegra234_main_ports in drivers/gpio/gpio-tegra186.c). The GPIOs
>> are assigned a index by the kernel from 0-163, but these GPIOs are
>> not contiguous with respect to the device-tree specifier.
>
> If I may ask...
>
> Why? Is it sparse because there are pads that can't be used as GPIOs?

It is purely how the different port for the GPIO controller are
configured in h/w ...

static const struct tegra_gpio_port tegra234_main_ports[] = {
TEGRA234_MAIN_GPIO_PORT( A, 0, 0, 8),
TEGRA234_MAIN_GPIO_PORT( B, 0, 3, 1),
TEGRA234_MAIN_GPIO_PORT( C, 5, 1, 8),
TEGRA234_MAIN_GPIO_PORT( D, 5, 2, 4),
TEGRA234_MAIN_GPIO_PORT( E, 5, 3, 8),
TEGRA234_MAIN_GPIO_PORT( F, 5, 4, 6),
TEGRA234_MAIN_GPIO_PORT( G, 4, 0, 8),
TEGRA234_MAIN_GPIO_PORT( H, 4, 1, 8),
TEGRA234_MAIN_GPIO_PORT( I, 4, 2, 7),
TEGRA234_MAIN_GPIO_PORT( J, 5, 0, 6),
TEGRA234_MAIN_GPIO_PORT( K, 3, 0, 8),
TEGRA234_MAIN_GPIO_PORT( L, 3, 1, 4),
TEGRA234_MAIN_GPIO_PORT( M, 2, 0, 8),
TEGRA234_MAIN_GPIO_PORT( N, 2, 1, 8),
TEGRA234_MAIN_GPIO_PORT( P, 2, 2, 8),
TEGRA234_MAIN_GPIO_PORT( Q, 2, 3, 8),
TEGRA234_MAIN_GPIO_PORT( R, 2, 4, 6),
TEGRA234_MAIN_GPIO_PORT( X, 1, 0, 8),
TEGRA234_MAIN_GPIO_PORT( Y, 1, 1, 8),
TEGRA234_MAIN_GPIO_PORT( Z, 1, 2, 8),
TEGRA234_MAIN_GPIO_PORT(AC, 0, 1, 8),
TEGRA234_MAIN_GPIO_PORT(AD, 0, 2, 4),
TEGRA234_MAIN_GPIO_PORT(AE, 3, 3, 2),
TEGRA234_MAIN_GPIO_PORT(AF, 3, 4, 4),
TEGRA234_MAIN_GPIO_PORT(AG, 3, 2, 8),
};

Each port can have upto 8 pins, but some don't. Note the last number in
the column indicates the number of pins for a port.

>> For example, in device-tree, if I have a shared-gpio with the
>> following specifier ...
>>
>> gpios = <&gpio TEGRA234_MAIN_GPIO(AF, 1) GPIO_ACTIVE_LOW>;
>>
>> The macro TEGRA234_MAIN_GPIO(AF, 1) evaluates to (23 * 8) + 1 = 185.
>
> To me it sounds like a bad design of the driver for this SoC/platform.

I am not sure why you think that. Assuming a 1:1 mapping of the kernel's
GPIO index to the GPIO controller + h/w port + 1 GPIO number seems fragile.

Jon

--
nvpublic