Hi,
On 20/11/2019 15.34, Peter Ujfalusi wrote:
> Hi,
>
> The initial support can replace all use of GPIOD_FLAGS_BIT_NONEXCLUSIVE if the
> shared GPIO is configured to follow pass through 'strategy' for the shared GPIO
> pin.
>
> I have only implemented DT support.
>
> With the shared gpio support one can choose between three different strategy for
> managing the shared gpio:
> refcounted low: Keep the line low as long as there is at least one low
> request is registered
> refcounted high: Keep the line high as long as there is at least one high
> request is registered
> pass through: all requests are allowed to go through without refcounting.
>
> Few shortcomings as of now:
> - can not handle different GPIO_ACTIVE_ on the user side, both the root GPIO
> (which is shared) and clients must have the same GPIO_ACTIVE_ mode.
> We are using common gpio_desc.
> Like with GPIOD_FLAGS_BIT_NONEXCLUSIVE
> - refcounting counts _all_ 1/0 requests coming from the users of the shared
> GPIO. This could cause issues if clients are using the gpiod API in unbalanced
> way.
> We would need to have separate tracking for each of the clients and agregate
> the level they are asking for at any moment. Basically a new gpio-chip on top
> of the real gpio pin can solve this.
I forgot to add an example for DT.
I have this for two pcm3168a codec, their RST pin is connected to
tca6416's p0 pin.
The codec's RST line is low active, so the gpio-shared is configured to
refcounted high to make sure that a codec is not placed in reset when it
does not want it.
&main_i2c3 {
#address-cells = <1>;
#size-cells = <0>;
audio_exp: gpio@21 {
compatible = "ti,tca6416";
reg = <0x21>;
gpio-controller;
#gpio-cells = <2>;
p00 {
gpio-shared;
gpios = <0 GPIO_ACTIVE_LOW>;
output-high;
refcounted-high;
line-name = "CODEC RESET";
};
};
pcm3168a_a: audio-codec@47 {
compatible = "ti,pcm3168a";
reg = <0x47>;
#sound-dai-cells = <1>;
reset-gpios = <&audio_exp 0 GPIO_ACTIVE_LOW>;
};
pcm3168a_b: audio-codec@46 {
compatible = "ti,pcm3168a";
reg = <0x46>;
#sound-dai-cells = <1>;
reset-gpios = <&audio_exp 0 GPIO_ACTIVE_LOW>;
};
};
>
> Regards,
> Peter
> ---
> Peter Ujfalusi (2):
> dt-bindings: gpio: Document shared GPIO line usage
> gpiolib: Support for (output only) shared GPIO line
>
> .../devicetree/bindings/gpio/gpio.txt | 66 +++++++++
> drivers/gpio/gpiolib-of.c | 28 +++-
> drivers/gpio/gpiolib.c | 132 ++++++++++++++++--
> drivers/gpio/gpiolib.h | 10 ++
> 4 files changed, 223 insertions(+), 13 deletions(-)
>
- Péter
Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
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