Re: Question about ASPEED GPIO value/direction set order

[Nikita Shubin <nikita.shubin@maquefel.me>]

Hi Andrew, thank you for quick answer.

The reason i am asking this is that in QEMU the first time we set pin,
all below if (diff) in aspeed_gpio_update() won't be triggered due to
direction is set after the value itself (so no qemu_set_irq()
triggers):

https://elixir.bootlin.com/qemu/v9.2.2/source/hw/gpio/aspeed_gpio.c#L314

aspeed # gpioset 0 8=1
aspeed_gpio_write offset: 0x1c value 0x100
aspeed_gpio_write offset: 0x0 value 0x100       <-- VALUE
aspeed_gpio_write offset: 0x4 value 0x100       <-- DIRECTION

And i doubted if it's a QEMU or Linux driver flaw.

Thank you for the clarification!

On Thu, 2025-03-13 at 16:51 +1030, Andrew Jeffery wrote:
> Hi Nikita,
> 
> On Tue, 2025-03-11 at 15:40 +0300, Nikita Shubin wrote:
> > Hi Joel and Andrew !
> > 
> > I am observing "strange" behaviour when pin direction is set AFTER
> > the
> > value itself:
> > 
> > ```
> > aspeed_gpio_dir_out:
> > 
> > __aspeed_gpio_set(gc, offset, val);
> > gpio->config->llops->reg_bit_set(gpio, offset, reg_dir, 1);
> > ```
> > 
> > Is this as intended ?
> 
> Yes; you tend to set the value only when using the GPIO for output,
> and
> by setting the value before setting the direction, we avoid the
> potential value glitch which occurs under the opposite order.
> 
> Andrew
>